REPORT NO. FAA-RD-75-120.il AIRPORT SURFACE TRAFFIC CONTROL CONCEPT FORMULATION STUDY VOLUME II - OPERATIONS ANALYSIS OF O'HARE AIRPORT - PART I F. D'ALESSANDRO W. HEISER G. KNIGHTS P. MONTELEON R. REFFELT R. RUDMANN W.WOLFF | AT10N \PR.2S1976 NORTHWESTS (IHIVE^SITY JULY 1975 LIBRARY FINAL REPORT DOCUMENT IS AVAILABLE TO THE PUBLIC THROUGH THE NATIONAL TECHNICAL INFORMATION SERVICE. SPRINGFIELD, VIRGINIA 22161 Prepared for U. S. DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION Systems Research and Development Service Washington, D.C. 20591 NOTICE This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Govern- ment assumes no liability for its contents or use thereof. NOTICE The United States Government does not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of this report. Te^rirjicol Keoort Documtnidtinn Poge 4. Title and Subtitle ^AIRPORT SURFACE TRAFFIC CONTROL CONCEPT FORMULATION STUDY Volume n - Operations Analysis of O'Hare Airport- Part I 'FAA-RD FAA-RD-75-120.il 7. Author'.) F> DTAlessancjro, W. Heiser, G. Knights, P. Monteleon, R. Reffelt, R. Rudmann, W. Wolff 3 5556 029 297231 July 1975 6. Performing Oroon, «otion Cod. 9. P.rfo'mng Oreonnotion Report N DOT-TSC-FAA-75-8. 1 1 Performing Orgoni jotion Nome ond Address Computer Sciences Corporation* 6565 Arlington Boulevard Falls Church, VA 22046 10. Work Un.i No (TRAIS) FA321/R6134 DOT-TSC-678 13. Type of Report ond 12. Sponsoring Agency Nome ond \ddrei* U. S. Department of Transportation Federal Aviation Administration Systems Research and Development Service Washington. DC 20591 : Final Report September 1973-February 1975 14. Sponsoring Agency Co< *Under contract to: U. S. Department of Transportation Transportation Systems Center, Kendall Square, Cambridge MA 02142 This four volume report presents system concepts for use in semi-automated airport sur- face traffic control at all positions in the tower cab of the major airports. The control functions and data requirements of a Ramp Control System, a Ground Control System, and a Local Control System are presented. The concept development process has been based upon an extensive study of cab operations at O'Hare Airport. This effort has in- cluded extensive delay analysis, study of communication tapes, and personal observations of the widely- varying situations that are faced by tower controllers. Following the Opera- tions Analysis effort, a detailed study of requirements was performed and is presented in Volume IV of this report. This requirements effort provided an estimate of the perform- ance requirements of a surveillance sensor that would be required in a TAGS (Tower Automated Ground Surveillance) system for use in both good and poor visibility condi- tions. Detailed studies were made of the complex type of conflicts to be solved by both the Ground and Local Controllers and operational levels and densities were developed. One particular TAGS system concept (employing an ATCRBS Trilateration Surveillance Subsystem) is described in Volume I and an estimate is made of its deployment potential at major airports. Backup material on this concept in the form of a working paper is held by TSC. This working paper also includes synthetic digital display concepts for the three systems which have been summarized in Volume I. 17. K.y word. Airport delays, requirements capacity analysis, communications, syn- thetic displays, ATCRBS Trilateration, deployment estimates DOCUMENT IS AVAILABLE TO THE PUBLI THROUGH THE NATIONAL TECHNICAL INFORMATION SERVICE, SPRINGFIELD, 19. Seconty Clo.s.f. (of th.» rep, Unclassified Form DOT F 1700.7 (8-72) 20. Security Clns.i'. [of thi s pa, Unclassified Reproduction of completed pnge ISKA8H "• I/. 2- At tower-equipped airports, the controllers in the tower cab are responsible for those aspects of Airport Surface Traffic Control (ASTC) requiring centralized management: issuing clearances for aircraft to land, taxi, or take off; establishing routing patterns for arriving and departing aircraft on the runway/taxiway net- work so as to minimize delays; sequencing aircraft movements on runways and taxiways and at critical intersections to ensure safety; and controlling the movements of service or emergency vehicles on the airport surface. Because of the expertise of the controllers and pilots, the ASTC system has worked well most of the time. However, the unfortunate incidents at Chicago-O'Hare (20 December 1972) and Boston-Logan (31 July 1973) have pointed out certain deficiencies; e.g. , the system's surveillance capability when visibility is poor. Initiated by the Federal Aviation Administration (FAA), the ASTC program is in the process of implementing several near-term system improvements. However, it is expected that these improve- ments, while adequate for the 1970's, will not be adequate to meet the more stringent long-term requirements of the 1980 's. The approach which has been taken in the present study is to con- centrate on the Nation's most active and, in one sense, most mature airport; i.e. , Chicago-O'Hare. In performing the study at O'Hare, the cooperation of the Airport Traffic Control Tower, the City of Chicago Department of Aviation, and the FAA Great Lakes Region was essential to the success of the effort. Mr. Paul S. Rempfer, of the Transportation Systems Center (TSC), acted as technical monitor for the Government. In addition, Messrs. Rempfer and L. Stevenson, also of TSC, performed the theoretical analysis of local area capacity which is presented in Section 5. 3. 3. 1 of Volume III. Digitized by the Internet Archive in 2012 with funding from CARLI: Consortium of Academic and Research Libraries in Illinois http://www.archive.org/details/airportsurfacetr02dale TABLE OF CONTENTS - VOLUME II Section 1 - Introduction 1.1 General 1.2 Overview of Study 1. 3 Description of Operations Analysis Section 2 - Operations Analysis Approach 2-1 2.1 General 2-1 2.2' Establishing the Basis for Analysis 2-1 2. 3 O' Hare Operations Effectiveness Analysis Approach 2-8 2.3.1 General 2-8 2.3.2 Fuel Consumption Assessment 2-9 2.3.3 Operating Cost 2-11 2.3.4 Passenger Inconvenience Assessment 2-12 2.3.5 Summary of Effectiveness Measures 2-14 2.4 Methodology for Functional Analysis of ASTC System Operation 2-16 2.4.1 Controller Task Analysis 2-19 2.4.2 Aircraft Flow Analysis 2-28 2.4.3 Airline Operations Analysis 2-36 2.4.4 Airport Management Operations Analysis 2-40 2.5 Projection of the Future Operating Environment at O'Hare Airport 2-41 Section 3 - Airport Configuration Description 3-1 3. 1 General 3-1 3. 2 Runway Configuration Description 3-1 3.2.1 Runway Descriptions 3-1 3. 2. 2 Runway Configuration Usage 3-6 3.3 Taxi Flow Patterns 3-23 3.3.1 Configuration 1 3-24 3. 3. 2 Configuration 2 3-29 3. 3. 3 Configuration 3 3-31 3.3.4 Configuration 4 3-33 3.3.5 Configurations 3-35 3.3.6 Configuration 6 3-37 3. 3. 7 Configuration 7 3-37 3.3.8 Configurations 3-40 3.3.9 Configuration 9 3-42 3. 3. 10 Configuration 10 3-44 TABLE OF CONTENTS - VOLUME II (Continued) Page 3. 3. 11 Configuration 11 3-44 3.4 Terminal Configuration Description 3-48 3.4.1 Terminal Gate Layout 3-48 3.4.2 Aircraft Docking at the Gates 3-51 3.4.3 Aircraft Movements and Control 3-51 3.4.4 Impact of Terminal Configuration on ASTC System Operation 3-52 Section 4 - Functional Description of the O'Hare ASTC System 4-1 4.1 General 4-1 4. 2 FAA Airport Traffic Control Tower (ATCT) Functions 4-1 4. 2. 1 General Responsibilities 4-1 4.2.2 Tower Cab 4-2 4.2.3 TRACON 4-69 4. 3 Airline Functions 4-74 4.3.1 General Responsibilities 4-74 4. 3. 2 Airline Terminal Operations 4-75 4.3.3 Flight Deck (Cockpit) Operations 4-84 4.4 Airport Management Functions 4-88 4.4.1 General Responsibilities 4-88 4.4.2 Airport Personnel Position Descriptions 4-88 4.4.3 Functional Operations Description 4-92 4.4.4 Emergency Operations 4-97 LIST OF ILLUSTRATIONS - VOLUME II 1-1 Task Breakdown and Study Flow 1-2 1-2 Simplified O'Hare Operations Analysis Flow Diagram 1-5 2-1 Departure Flight Operations Flow 2-3 2-2 Arrival Flight Operations Flow 2-4 3-1 Current O'Hare Layout 3-2 3-2 Location of Departure Queues and Ground Control Handoff Areas at O'Hare 3-25 3-3 Aircraft Routes at O'Hare - Hangar, Cargo and Air Force Areas 3-26 3-4 Main Service Vehicle Roads at O'Hare Airport 3-27 3-5 Configuration 1 3-28 3-6 Configuration 2 3-30 3-7 Configuration 3 3-32 3-8 Configuration 4 3-34 3-9 Configuration 5 3-36 3-10 Configuration 6 3-38 3-11 Configuration 7 3-39 3-12 Configuration 8 3-41 3-13 Configuration 9 3-43 3-14 Configuration 10 3-45 3-15 Configuration 11 3-46 3-16 Gate Assignments 3-49 4-1 O'Hare Control Tower Floor Plan 4-3 4-2 Tower Cab Detail 4-4 4-3 Tower Cab Photographs 4-10 4-4 Visual Surveillance Limitations 4-30 4-5 Radar Coverage 4-32 4-6 Functional Flow of Major Flight Data Tasks 4-34 4-7 Functional Flow of Clearance Delivery Tasks 4-39 4-8 Functional Flow of Major Outbound Ground Tasks 4-45 4-9 Functional Flow for Major Inbound Ground Tasks 4-56 4-10 Functional Flow of Major Local Control Tasks 4-61 4-11 TRACON Room - O'Hare International Airport 4-70 4-12 United Airlines Gate Plan for O'Hare Airport 4-77 4-13 VHF Radios in Cockpit 4-85 4-14 Chicago - O'Hare International Airport Organization Chart 4-89 LIST OF TABLES - VOLUME II Table Page 2-1 Summary of Effectiveness Measures 2-15 2-2 Examination of Aircraft Flow Variables 2-27 2-3 Movement Events Measured for ASDE Film Analysis 2-30 3-1 Classification of Crossing Runway Configurations 3-3 3-2 Runway Landing Aids at O'Hare 3-5 3-3 Primary Runway Configurations Identified by ATCT 3-8 3-4 Runway Usage Minimums Under Low Visibility Conditions 3-11 3-5 0"Hare Runway Utilization CY-71 3-13 3-6 Seasonal Runway Configuration Usage (January and February 1973) 3-15 3-7 Seasonal Runway Configuration Usage (April and June 1973) 3-16 3-8 Profile of Runway Configurations Used in Clear and Calm Weather 3-19 3-9 Profile of Runway Configurations Used in Unclear and/or Windy Weather 3-20 3-10 Relative Usage of Various Runway Configuration Classes at O'Hare 3-22 3-11 Gate Assignments Vs Ramp Areas at O'Hare 3-50 4-1 Responsibilities and Duties of the Flight Data Postion 4-16 4-2 Responsibilities and Duties of Clearance Delivery Position 4-17 4-3 Responsibilities and Duites of Outbound Ground Position 4-19 4-4 Responsibilities and Duties of Inbound Ground Position 4-21 4-5 Responsibilities of Local Control Position 4-23 4-6 Clearance Delivery Gate Marking 4-41 4-7 Predominantly Preferred Checkpoints for Position Reporting During Low Visibility Conditions 4-50 4-8 Specific Points or General Areas at Which Turnover to Local Control May be Made by Outbound Ground 4-53 4-9 Responsibilities and Duties of the Approach Control Position 4-71 4-10 Responsibilities and Duties of Departure Control Position 4-72 4-11 Responsibilities and Duties of Parallel Approach Monitor 4-73 4-12 Authorized Aircraft Parking -- O'Hare Passenger Terminal — American Airlines 4-80 SECTION 1 - INTRODUCTION 1. 1 GENERAL This working paper describes and presents the results of the first phase of the Advanced Airport Surface Traffic Control (ASTC) Systems Concept Formulation Study conducted for the Transportation Systems Center (TSO under Contract DOT-TSC-678. The report describes the approach followed and the anal- ysis techniques employed in the performance of the operations analysis of the cur- rent ASTC system for the baseline airport, O'Hare International Airport, Chicago, Illinois. It also describes the data resulting from this analysis to draw conclusions on the effectiveness of the current ASTC system operations at O'Hare and on the effectiveness of the system in projected future operational environments at O'Hare. The remainder of this introductory section is intended to provide a reference for the descriptions of the study presented in Sections 2 through 6 and the summary and conclusions presented in Section 7. Section 1. 2 provides an overview description of the Concept Formulation Study to place the O'Hare Opera- tions Analysis in context. Section 1. 3 then provides a brief description of the ap- proach followed in the operations analysis. 1. 2 OVERVIEW OF STUDY The basic objectives of the Concept Formulation Study are to: 1. Define and evaluate functional and design concepts for potential future ASTC systems configurations. 2. Estimate the potential for deployment of the alternative system configurations at airports in the National Airport Systems Plan (NASP). The overall approach adopted for the study to achieve these objectives is illustrated in a simplified manner in Figure 1-1. This approach represents an organization of technical studies providing a logical and stepwise methodology for characterization of ASTC system concepts and evaluation of these concepts as a basis for estimation of the nature of systems which may be deployed at NASP air- ports in an orderly and cost-effective manner. 3E ED v> o 2*£ 5 o »3« si El S<3 «* <=> o Q • • 5 " In essence, the study structure represents four technical analysis phases. The first three tasks shown comprise the airport operations analysis phase which is the subject of this working paper. This phase is intended to provide data from which an understanding of airport operations and operational needs can be developed. This includes a comprehensive and detailed characterization of the interrelationships between various organizations and individuals involved in air- port operations and areas in which these interrelationships might be enhanced by future ASTC systems to increase the effectiveness of airport operations. Thus, this phase serves as a baseline for the subsequent study efforts. The objective of the second phase of the study (Task 4 - Module De- scriptions and Benefits Estimated will be to define, examine, and evaluate func- tional performance concepts for potential ASTC system configurations. The under- standing of airport operations and operational needs developed in Phase 1 provides a reference for definition of future ASTC systems on a modular configuration basis; that is, conceptual structuring of future systems as the integration of a number of system modules, each intended to support a specific functional performance require- ment of an ASTC system. In addition, preliminary requirements analyses, system de- scriptions , and data collected at two other airports (Boston-Logan and Hartford-Bradley Field) already completed apart from this contract will be provided by the Government and utilized to avoid site specific modules. Each functional module will be defined in terms of the capabilities to be provided and its interrelationship with other system mod- ules and external interfaces. Utilizing the quantitative data on system operations developed in Phase 1, estimates of the performance and economic benefits of the achievement of these functional capabilities will be developed. The objective of the third phase (Task 5 - Mechanization Descriptions and Cost Estimates) will be to define, examine, and estimate the costs of functional design concepts for system modules; that is, conceptual structuring of the design of system modules as the integration of a number of hardware/software elements required to provide the functional capabilities defined for the modules in Phase 2. Design concepts will be developed for mechanizing the system modules by alterna- tive equipment technologies (for example, digitized radar or trilateration on ATCRBS transponders) and the costs associated with these alternative approaches estimated. The objective of the fourth phase of the study (Task 6 - Deployment Analysis) will be to estimate the deployment potential for the various system design approaches defined in Phase 3; that is, estimation of the number of ASTC modules mechanized by each of the alternative equipment technologies that could be imple- mented at airports in the NASP on a cost-effective basis. This estimation will draw upon the understanding of airport operations and operational needs developed in Phase 1 to define ASTC functional capabilities that would be required at various NASP airports as a function of time. The estimation will also draw upon under- standing of performance and economic benefits of various module functional capa- bilities developed in Phase 2 and the costs of achieving those functional capabilities by alternative technological approaches as defined in Phase 3. This background understanding and data base will be combined to identify the types of ASTC systems which would be implemented that would most cost-effectively meet the needs of various airports and from this the total development potential for implementation of system modules by the competing technologies. 1. 3 DESCRIPTION OF OPERATIONS ANALYSIS The technical approach taken in the O'Hare operations analysis is illus- trated in a simplified manner in Figure 1-2. As a point of departure for the operations analysis a preliminary ex- amination of the ASTC system operation at O'Hare was performed using informa- tion readily available. Primary sources of this information were documentation and materials provided by TSC at the initiation of the contract including maps, ASDE films, and communications recording tapes made by TSC in February/March 1973, and a copy of the O'Hare Airport Air Traffic Control Tower (ATCT) Training Manual. The ASDE films were briefly reviewed to gain an impression of the fc ^ A 1 8 J s .1 traffic flow patterns for the various runway configurations observed. Similarly, communications recordings for the several air traffic controller positions in the tower cab and airline company communications were listened to in order to gain an impression of the basic nature and noticeable differences in the manner in which aircraft movements were controlled. These reviews were made against the back- ground of maps of airport surface configuration and the description of controller activities provided in the Training Manual. Based upon these activities, prelimi- nary flow diagrams outlining the estimated flow sequence for departure and arrival aircraft were developed. The sequence definitions included the various communi- cations and control actions that might be expected to occur in an aircraft's move- ments. These preliminary operational definitions provided the basis for the definition of the approach to be followed in assessing the effectiveness of the O'Hare ASTC system. Criteria against which the system effectiveness would be evaluated were first identified. Various methods of measuring the effectiveness criteria were considered and the most practical measures selected. The resulting effec- tiveness criteria were divided into two groups, those which could be directly meas- ured from operational flow data and those which could be measured indirectly (i. e. , as extrapolations of the directly measured criteria variables). Directly measur- able criteria included: traffic flow statistics (e.g. , delay time per operation), controller workload (e. g. , communications channel occupancy time), and pilot workload (e. g. , communications time per operation). The decision was made to utilize traffic flow statistics as the directly measurable criteria for the extrapola- tion of indirectly measured effectiveness criteria. Thus, examples of these indi- rect criteria included operational cost increase (delay time x cost of operation per unit of time), incremental pollution emission (delay time x pollution emission rate per unit of time), passenger inconvenience (delay time x passengers delayed). It was also decided that accident risk represented an important variable for effective- ness evaluation but that a direct measurement of accident risk was not feasible. Therefore, accident risk was considered as an indirect criteria to be measured in terms of such measurable parameters as the lack of visibility of operations in certain areas or number of missed instructions. The two preceding activities served as the basis for development of a Data Collection and Analysis Plan. The plan identified the data required to support the effectiveness criteria measurement, the means for collection of the data, and the methods for extraction and reduction of the data collected. In developing the plan the TSC collected ASDE films and communications recordings were reviewed again in further depth to identify the data which could be extracted from each and the most logical procedures for this extraction and reduction. A determination was made that the collection of additional data was required for several reasons including: the need to obtain clear recordings of ground controller channels*, ac- quisition of data for periods of Category I and II operations, and the need to obtain data on aircraft movements within the ramp/gate areas (which could not be derived from the ASDE films). A brief survey visit was made to O'Hare to derive informa- tion needed for finalization of the plan. The major objectives of this survey were to: 1. Obtain brief descriptions of the general procedures followed by the various controller positions and identify areas in which spe- cific information on the variations in general controller proce- dures must be obtained through controller interviews and obser- vations in the tower cab. 2. Identify locations from which traffic movements within the ramp/ gate areas could be observed and recorded. 3. Test various methods for improved communications channels re- cording as a basis for design and fabrication of any special equip- ments necessary for this purpose. The Data Collection and Analysis Plan was then finalized and materials for the collection, extraction, and reduction of the data developed including: *Because of the method of recording employed, there was substantial interference between Outbound (departure) Ground and Inbound (arrival) Ground or clearance delivery communications recorded on the tapes. • Log forms for the extraction and reduction of data from ASDE films and communications tapes • Log forms for observation/recording of system operations in the tower cab and ramp/gate area • Preliminary controller interview questionnaire • Questionnaires for interviews of airline gate scheduling/manage- ment personnel, pilots, and O'Hare Airport management person- nel. The Data Collection and Data Reduction and Analysis activities were then initiated in parallel. Within the Data Collection effort, considerable attention was devoted to detailed interviews with several tower cab controllers to obtain descriptions of the specific procedures followed in their operations at the various positions in the tower cab and their criteria for applying the procedures (e. g. , the criteria applied in routing aircraft to or from the runways in use where alternative routes are possible). In addition, the interviews were designed to solicit comments from the controllers on potential functional concepts for future ASTC systems for use in the second phase of the study. 1. The conduct of interviews with gate scheduling/control personnel pertaining to personnel responsibilities and procedures followed in managing gate operations. 2. The conduct of interviews with pilots pertaining to the responsibil- ities and procedures followed by flight officers in the operation of aircraft. 3. Utilization of United Airlines and American Airlines control towers for the observation of ramp/gate area traffic operations. 4. Flight Deck Authority for United Airlines aircraft for the purpose of observing cockpit operations at first hand. Interviews were also conducted with O'Hare Airport management per- sonnel to determine the responsibilities and procedures followed by functional units in maintaining the operating condition of the Airport and coordinating the operations of the units with the ATCT. The additional operations data collection was performed and included periods of simultaneous ASDE film, controller communications recording, obser- vation and recording of traffic movements in the ramp/gate areas, and observation and recording of controller activities in the tower cab. The initial activities in Data Reduction and Analysis were directed toward the analysis of selected ASDE films and communications recordings made by TSC. Attention was focused on the analysis of selected periods with varying traffic operations rates under visual operation conditions for runway configurations representative of the normal easterly and westerly operations modes of the airport. The resultant data was intended to serve as a background for further analyses of the impact of weather conditions on O'Hare operations. As the information col- lected by CSC personnel in the field became available it was reduced and inter- preted for application in developing narrative and quantitative descriptions of O'Hare operations. The quantitative data developed in the preceding activity was compiled for application in the System Effective Analysis of the current O'Hare operating environment and projected future operating environments. A review of the approach defined earlier for the effectiveness analysis was made against the background of this data and other information acquired during the preceding efforts; in particular, a deeper understanding of the O'Hare operational processes and suitable adjust- ments to that approach were made. Because reliable data on future changes to the operating environment at O'Hare could not be obtained in the form required for the planned approach, cer- tain assumptions were made regarding future modification of the airport configura- tion. No attempt was made to quantitatively extrapolate the impact of these changes. However, qualitative assessments of the impact of these changes, particularly with respect to ground taxi and departure delays, were made. With respect to the subject of accident risk, situations observed of the ASDE film analysis and the understanding of O'Hare operations developed through the field activities were drawn upon to develop qualitative assessments of poten- tially hazardous situations which merit attention and possible near term correction through ASTC system improvements. The plans, procedures followed, and results developed in all the pre- ceding activities served as the basis for the preparation of this working paper. SECTION 2 - OPERATIONS ANALYSIS APPROACH 2. 1 GENERAL The purpose of this section is to describe in detail the technical ap- proach followed in performing the operations analysis and effectiveness analysis for the O'Hare ASTC system and the rationale for this approach. 2. 2 ESTABLISHING THE BASIS FOR ANALYSES As the first step taken, a preliminary definition of the ASTC system operation was developed. Maps of the O'Hare Airport configuration were studied to become familiar with the layout of the runways and taxiway network. The Chicago O'Hare Airport Air Traffic Control Tower (ATCTi Train- ing Manual was reviewed to obtain a general understanding of the responsibilities and duties of the tower cab positions and of positions in the TRACON as they inter- face with the airport operations. The Manual includes maps illustrating a number of basic runway utilization configurations and associated taxi flow patterns which provided a basic understanding of operational flow patterns. This understanding was further developed by review of a number of ASDE films taken by TSC in February and March, 1973. The films were studied to further examine the traffic flow for the various specific operational configura- tions in relation to: 1. Emanation of traffic from or exit to the passenger terminal 2. Taxi to and from the various runways in use 3. Aircraft delays or stops enroute to or from the runways 4. Departure aircraft queuing for the various runways 5. Interleaving of departures and arrivals in cases of mixed opera- tions on the same runway and in separated operations on crossing runways Controller and airline communi cations channel recordings made by TSC simultaneously with the ASDE films were reviewed to gain an impression of the communications between tower and airline personnel. Brief periods of the communications recording tapes for various controller positions and airline chan- nels corresponding to the ASDE films previously reviewed, where available, were listened to for the purpose of generally classifying: 1. The stages in the aircraft flow in which communications take place with the various operational personnel 2. The nature of the communications control discipline followed 3. The nature of the information transmitted by the various person- nel involved 4. Any distinctions between control procedures and associated com- munications arising from the operating configuration and condi- tions Based upon the preceding activities, simplified flow charts illustrating the basic stages of the passage of aircraft through the system were developed for both departure and arrival operations. The flow charts are illustrated in Figures 2-1 and 2-2 for departure and arrival operations, respectively. Superimposed on these diagrams are indications of the controller positions involved in the process- ing of the aircraft throughout the various stages of operation. The purposes in developing these flow charts were twofold. The first was to provide a continuing reference for project personnel in the subsequent in- vestigations of the ASTC operation. The second, and more important, was to serve as the basis for defining the approach to be followed in studying the ASTC system and analyzing the effectiveness of its operations. The flow charts were examined to identify: 1. Stages at which the flight could experience delays in its process- ing. 2. Areas in which detailed investigation of the procedures followed at controller positions was essential in understanding the ASTC system operation, developing qualitative workload estimates, and formulating concepts for future ASTC systems. 3. Areas in which detailed investigations of the procedures followed by airline operations and flight personnel were essential in under- standing terminal facilities usage and pilot information require- ments in relation to aircraft control, and in formulating concepts for future ASTC systems. 4. Stages of operation at which reduced visibility conditions impact on the system and specific areas of investigation to quantify this impact on various system operational personnel. 5. Stages of operation at which there is a risk of accident and spe- cific areas of investigation to qualitatively or quantitatively exam- ine the potential hazards. As an example, the stages of operation at which aircraft could experi- ence delays identified by the review are outlined heavily in Figures 2-1 and 2-2. The results of the review then served as the basis for the following: 1. Preliminary definition of criteria and measures for assessment of the ASTC system effectiveness 2. Definition of the data required for the defined system effectiveness analysis approach 3. Preliminary identification of the appropriate sources of the data required and the means for extraction of the data from the sources 4. Identification of areas in which further clarification of operational procedures or potential data collection methods was necessary for finalization of the analysis plan. A survey visit was then made to O'Hare Airport to satisfy the informa- tion requirements identified in 4 above. The survey activities included: 1. Discussions with O'Hare ATCT personnel to determine the actual procedural flow of task activities for each controller position in the tower cab. The discussions identified both the basic procedural flow for each position and areas in which there is some variability in individual controller procedures which would have to be deter- mined through personnel interviews and observations in the tower cab. 2. Discussion of the problems encountered in the use of the current ASDE Brite equipments. It was learned that the ATCT had pre- viously determined the coverage limits of the equipments and that the results were presented on a map of the airport which would be provided for the study. 3. Testing of a new method for recording of controller communica- tions channels directly from the communications equipment to eliminate the problem of overlap and interference between the Outbound (departure) Ground and Inbound (arrival) Ground com- munications encountered on the TSC recordings. The design re- quirements for the equipments that would be required to accom- plish this without interference with FAA channels were worked out with ATCT personnel as inputs to the design and fabrication of the equipments. Based upon the results of this survey a Data Collection Analysis Plan was finalized. The data collection and analysis procedures followed in the subse- quent operations analysis based upon this plan are described in the following para- graphs. A major aspect of the plans for analysis of the O'Hare ASTC system was a decision to examine the airport operations in terms of two modes of opera- tion. Review of the ASDE films and associated data provided by TSC and the maps of runway/ taxiway usage configurations provided in the ATCT Training Manual in- dicated that O'Hare operations could essentially be divided into two modes. These modes were "Arrivals from the East" and "Arrivals from the West. " As informal discussions with ATCT personnel indicated that the arrival runways were selected first in determining the runway configurations to be employed under various oper- ating conditions, this approach in defining the modes of operations in this manner was reasonable. Thus, the ASTC system effectiveness analysis and supporting func- tional analysis approaches, described in the following Sections 2. 3 and 2. 4, were devised to provide an examination on this basis. Various TSC data collection runs and, subsequently, CSC data collection runs representing operations in these modes were selected for detailed analysis. 2. 3 O'HARE OPERATIONS EFFECTIVENESS ANALYSIS APPROACH 2.3.1 General This paragraph summarizes the approach and methodology developed to evaluate the effectiveness of ASTC Systems at O'Hare. The proposed methods have general applicability to other airports and will be useful in evaluating the effectiveness of new ASTC concepts and techniques. While the methods offer this broad capability for future evaluations , attempts to apply them must be accom- panied by a rather extensive data collection program at the site under evaluation. Specifically, the data collection and reduction procedures used at O'Hare and dis- cussed throughout this report must be employed to accomplish the effectiveness evaluation at other airports. The objective of this analysis is to assess effectiveness by combining measured airport data with statistical considerations at O'Hare in order to evaluate the following derived effectiveness parameters: • Fuel Consumption • Operating Costs • Passenger Inconvenience This is accomplished by reducing raw data into a form which will pro- vide a direct measure of: • Airport surface holds, delays and service time • Controller communications workload • Cockpit crew communications workload 0 Communications incidents These direct measures are analyzed in conjunction with the following statistical considerations to determine a measure of effectiveness: Airport operational demand Airport weather profile Aircraft profile Airport operating modes Aircraft engine fuel consumption factor Aircraft operating cost factor Aircraft loading factor This analysis permits the calculation of a numerical effectiveness score(s) for each derived parameter. Since these parameters are not independent and their relative significance is a highly subjective consideration, this method- ology stops short of providing a composite effectiveness score. Nevertheless, a combinatory method could be added in the future if a composite score is desired. This would involve assigning subjective weighting factors for each effectiveness parameter, calculating a weighted score, and adding the weighted scores of each parameter. The following paragraphs describe the general approach for the indi- vidual parameter analysis. Detailed calculations and measured data consistent with this approach are contained in Section 6 of this report. 2.3.2 Fuel Consumption Assessment In view of the energy crisis, minimization of aircraft fuel consumption is a reasonable ASTC System goal. This parameter is directly related to mea- sured and statistical factors which are related by the following overall formula [ST + HT] x m» (l) : Estimated actual gallons of fuel consumed by aircraft on the airport surface during a one hour measurement period ST = Measured total service time (i. e. , time for all AC to travel be- tween ramp and runway or runway and ramp without stopping) during a one hour measurement period HT = Measured total holding time (i. e. , time spent by aircraft in a holding status) during a one hour measurement period n. — = Ratio of a specific aircraft type to the total at O'Hare as deter- mined from the aircraft profile FF. = Fuel factor (i.e., the gallons of fuel consumed per idle engine minute for the ith aircraft type) This calculation will determine the estimated fuel consumption during a specific measurement period. It is important to specify the operating conditions which existed during the measurement period so that measured data which was obtained over a limited sampling period could be statistically extrapolated to an annual consumption factor. The important operating conditions for this extrapolation are: • Aircraft operations per hour (measured/desired) • Weather conditions (good/poor) • Runway modes (west/east arrivals) By specifying the actual measurement conditions and by recognizing the probability of having various conditions during the year, the annual fuel con- sumption could be estimated. Finally, it is important to identify the potential improvement which can be obtained through the use of an optimum ASTC System. This is accomplished by letting HT = 0 in equation (1) thereby providing an estimate of the minimum gallons of fuel required. By forming the ratio of annual minimum fuel to annual estimated actual fuel the ASTC system can be given a fuel consumption effectiveness score which would optimally equal unity. This analysis assumes a linear relationship between fuel consumption and aircraft surface travel delays. For the most part this assumption is reason- able; however, it is possible that an ASTC system could be devised wherein this was not the case (viz. , a system where tugs or cables transport aircraft to and from the runway). Another consideration is the fact that limited fuel supplies could make the impact of a fuel-saving ASTC System much more significant. For example, it could easily determine whether or not airlines could also determine the number of flights that an airline could schedule and thereby control its business potential. In summary, while the linear relationship is reasonably valid, the impact of fuel conservation measures could exhibit effectiveness discontinuities which make fuel-saving ASTC systems even more attractive than this methodology indicates. 2.3.3 Operating Cost Airline operating costs are directly proportional to surface traffic delays since many of the elements which comprise this cost are based on the time between unblocking and blocking the aircraft at the gate, e.g. , crew hours, engine hours. To a certain degree surface traffic delays can be attributed to the airline itself as a result of ineffective gate control and scheduling. For the most part, however, these delays can be attributed to the ASTC System of the airport under evaluation. For this analysis airline operating costs will be estimated on a per aircraft type basis. These costs include: crew costs (salary /overhead) , fuel and oil, insurance, taxes, air frame maintenance, engine maintenance, deprecia- tion, rentals, maintenance burdens, and other miscellaneous expenses associated with the time an aircraft is in use. Not included are estimates for the ticketing system, reservation system, management, gate fees, etc. Airline operating cost will be computed from the formula: = [ST + HT] x 15- OC = Estimated total actual cost per test hour and CF. = Average airline cost in dollars per block minute for the ith aircraft type The estimated actual value for a specified measurement period was statistically extrapolated to an annual estimate. In addition, by letting HT = 0 in the formula, the minimum cost was determined such that the effectiveness score could be calculated as the ratio of the minimum to the actual annual cost. 2.3.4 Passenger Inconvenience Assessment Passenger inconvenience is a difficult parameter to assess, since inconvenience can vary considerably among passengers based on individual cir- cumstances. There are at least two airport surface travel factors which con- tribute to passenger inconvenience; however, the relative significance of these factors is not easily determinable. The general factors involved are: • Inconvenience due to delays • Inconvenience due to lack of comfort The delay factor is assessed by measuring the total ground delay time during a test hour and by using the formula PD.p =[HT] x n- PDACT = The total number of passenger delay minutes during the test hour PL. = The average passenger loading factor for the ith aircraft type The passenger delay effectiveness score is assessed by calculating the estimated actual passenger ground travel minutes for the year using the formula = [ST + HT] x i; and the statistical extrapolation factors. The minimum passenger travel minutes can be computed for the year by letting HT = 0. The effectiveness score is then determined as the ratio of the minimum to the actual annual passenger ground travel minutes. The comfort factor is assessed by measuring the number of starts and stops which the aircraft makes during airport ground travel using the formula = [2HN] x L-, n a and PCACT = Total number of passenger starts and stops during the test hour HN = The number of aircraft holds during the test hour Using the statistical extrapolation factors, the annual estimate for passenger starts and stops can be determined. The optimum value for this parameter is equal to zero. 2.3.5 Summary of Effectiveness Measures Table 2-1 provides a summary of the derived effectiveness parameters included in this effectiveness assessment methodology. The key measurement factors, the effectiveness measures, and the optimum effectiveness scores are also included for consideration. Section 6 demonstrates the application of these concepts to the evaluation of O'Hare ASTC effectiveness. J, to o « ft 0 a u ft ft o < o ft 1 o o H U < o Pi 1 Q ft ft U a* ft H U < o ft on Fh O "o ft "S 0) a CO d 0) ft""4 ft ^ o 1 SI £ ft h 8 c bj n D C «1 »1 S ra w 09 ft ft ft • • 2. 4 METHODOLOGY FOR FUNCTIONAL ANALYSIS OF ASTC SYSTEM OPERATION In performing the functional analysis of the O'Hare ASTC System oper- ation, the analysis activities were primarily directed toward developing the data required to support the ASTC system effectiveness analysis approach previously described. In essence, this required more than just the derivation of quantitative data describing aircraft movements and communications. It also required the de- velopment of an understanding of the environments, constraints, and procedures followed by the various operational personnel involved in the passage of aircraft through the ASTC System as a background for meaningful interpretation of the quantitative data. Thus, the development of the information base for the functional analysis of the ASTC System consisted of the collection, reduction, and analysis of operational movements and communications data and the conduct and analysis of interviews with representative samples of the operational personnel. The efforts in each of these areas for various aspects of the airport operation are described below. 2. 4. 1 Controller Task Analysis The controller task analysis effort was effectively divided into three distinct but related areas: interviews with representative controller personnel; controller communications recordings analysis; observation and analysis of physi- cal task activity. 2. 4. 1. 1 Controller Interviews Arrangements were made with the O'Hare ATCT and Great Lakes Re- gion for the availability of a number of representative tower cab controller person- nel to be available for in-depth interviews on traffic control procedures employed at the various controller positions. A draft Controller Interview Questionnaire was developed. The inter- view was designed to incorporate questions covering the operational procedures followed by the subject when operating the Clearance Delivery, Outbound Ground, Inbound Ground, and Local Control positions under normal (good) visibility condi- tions and poor visibility conditions. The opportunity was taken to include a number of questions intended to solicit controller opinions on potential functional perform- ance and design concepts for future ASTC systems. The interview was designed to be conducted verbally and included use of graphical representations of selected future ASTC System concepts. The draft interview was tested and recorded on tape for two control- lers. However, the interview with the second controller was terminated because of shortcomings of the draft questionnaire. Based on the experience gained by the interviews and difficulties experienced in attempting to transcribe the recording for the first controller, it was determined that revisions to the questions asked and method of recording the responses were required. A revised interview ques- tionnaire was developed. It consisted of two parts. The first was composed of questions to which simple responses could be expected and recorded directly on the interview form. The second was a written supplement composed of ques- tions for which the responses could be expected to be more extensive or complex and on which the controller would record his responses. This revised interview format was then employed for the second test controller and eight additional con- trollers. When completed, the interviews were analyzed to determine a com- posite of the results identifying the predominant response for the various ques- tions and the percentage of controller interviews providing this response. In many areas the controller responses were found to indicate a high degree of stand- ardization of procedures and decision criteria where alternative techniques might be applied. The results of this analysis served as a baseline reference for the controller communications analysis and, most particularly, for the observations of controller activities in the tower cab. A sample of the Controller Interview Questionnaire form employed is included in Appendix A. Completed interview questionnaires are included in the O'Hare Operations Analysis Data Supplement. 2. 4. 1. 2 Controller Communications Recordings Analysis Magnetic tape recordings of communications transactions between con- trollers and pilots (or surface vehicles) are uniquely useful in studying controller workload as these communications represent the major measurable element of his activity. Analyses of such recordings were performed to permit direct assess- ment of the controller communications activity and, in particular, for determina- tion of the amount of time spent in communications to all aircraft and to individual aircraft. The analysis identified in detail the nature of the communications in terms of the information transmitted between controllers and pilots and the vari- ous types of control disciplines employed by the various positions. Further, the data was derived in such a form as to permit limited extrapolation of the resultant data at the observed traffic levels to higher traffic levels for use in the future O'Hare ASTC system effectiveness analysis. To generate a data base for analysis, the tape recordings for various positions were examined in depth to classify the communications in terms of: 1. Individual communication transactions between controller and specific aircraft in chronological sequence. * 2. Message elements per communication transaction. The message element classifications were defined as the most descriptive re- garding the nature of the information transmitted within the trans- action. *A communications transaction was defined to include all the transmissions of both the controller and pilot necessary to complete the communication and any pauses in the conversations prior to its completion. 3. Primary communication transaction designations, i. e. , the pri- mary function of the transaction in terms of the message elements communicated, wherever possible. Message element classifications employed were derived from the communications analysis procedures currently in use by the FAA at NAFEC. These procedures are employed extensively in field studies of ATC facilities throughout the United States and in experimental studies at NAFEC. The rationale for selection of this approach is that it utilized well-defined standard definitions of ATC communications and would permit later comparison of the results of this study with studies of communications at other airports performed by NAFEC personnel. FAA message classification identifications were directly accepted or modified slightly to permit further refinements for the purposes of this study. For exam- ple, the basic FAA classification of a Control Instruction (Message Identification No. 110) was expanded to permit identification of aircraft sequence instructions or instructions related to penalty box holds by ground controllers as 111 and 112 identification numbers, respectively. The message element identifications and general classifications are listed below for the various controller positions. Clearance Delivery 180A Clearance requests by pilot 180B Clearance repeat requests or checks by pilot 180 Clearance delivery 180S Special clearance delivery (Communication contact by controller after initial contact) 150 Request to push back aircraft by pilot 210A Broadcast call for clearance requests by controller 210B Broadcast call for taxi requests by controller 230 Handover 310 Position reports 420 Taxi requests by pilots 450 Weather related communication 500 Communication incident (No response to call by controller or pilot) Inbound Ground Control 110 Control instruction (other than hold) 111 Sequence instruction (Instruction to follow another aircraft) 112 Penalty box or holding area instruction and advisories 120 Hold instruction 140 Yield instruction* (Instruction to control movement to yield right of way to another aircraft) 150 Clearance to pilot to enter ground control system 160 Clearance to pilot to enter ground control combined with hold instruction 310 Position report (Controller request and pilot response) 311 Destination or gate of incoming aircraft (a specific type of position report) 410 Traffic advisories 420 Taxi request by pilot wishing to move aircraft between hangar and terminal, etc. 470 Gate status information 500 Communication incident Outbound Ground Control 110 Control instruction 111 Sequence instruction 120 Hold instruction 140 Yield instruction 150 Clearance to pilot to enter ground control system *In the NAFEC message classification system this message identification is used for Speed Control instructions. This classification was adopted for the Yield In- struction since it is essentially an instruction to the pilot to adjust the speed of his aircraft's movement so as to permit another aircraft the right of way at an intersection. 160 Clearance to pilot to enter ground control combined with hold instruction 230 Handover 310 Position reports 410 Traffic advisories 500 Communication incidents Local Control 110 Control instruction (Runway turnoff or taxi) 120 Hold instruction 151 Takeoff clearance 152 Landing clearance 160 Clearance with runway hold (e. g. , position and hold) 230 Handover 310 Position reports 450 Weather reports (winds, visibility, etc. ) 500 / Communication incidents Communication transactions were timed out for each magnetic tape recording, usually of one hour duration. During the early stages of the communi- cations recording analysis an attempt was made to record the absolute start and stop time for each communications transaction. It was intended that these measure- ments would be used to: (1) compute the duration for each transaction; (2) provide a basis for statistical computation of the durations for various message types; (3) trace the aircraft between controller positions; and (4) match communications with air movements data in the ramp areas, taxiways, and runways. However, this was found to be extremely time consuming to accomplish satisfactorily and within the time and funds available. Thus, the procedure settled upon was to ac- cumulate, using a stop watch, the times spent in all communications transactions over a test period. The total communications activity time was then divided by the total of transactions to compute the average duration of a communications transaction. Examples of the communi cations transactions analysis form employed for each controller position is presented in Appendix A. The data obtained in the above data base generation was reduced to form the following parameters: 1. Clearance Delivery Average number of communication transactions (CT required per aircraft (AC) Average CT duration Percentage channel occupancy time required by transactions Average time lapse between first contact and handoff 2. Outbound Ground Control Average number of communication transactions (CT) required per aircraft Average CT duration Percentage time occupancy required by transactions Average number of required message elements per aircraft Average number of required control type instructions required per aircraft Number of departures per hour 3. Inbound Ground Control Average number of transactions required per aircraft Average CT duration Percentage time occupancy required by transactions Average number of message elements required per aircraft Average number of control type instructions required per aircraft Number of aircraft handled per hour 4. Local Control Average number of transactions required per aircraft Average CT duration Percentage time occupancy required by transactions Average number of message elements required per aircraft Aircraft handled/hour The large amount of magnetic tape data made available by TSC for February/ March 1973 was collected when the traffic volume was high. Unfortu- nately, thedatawas subject to adjacent channel interference. This was particularly so for the Ground Control positions, rendering reduction to be extremely difficult or impossible with accuracy. Therefore, only TSC Run #33 was analyzed for the Inbound Ground Control position from this source of data. Further recordings were made by CSC in January 1974 on smaller traffic volumes (due to reductions in scheduled operations based on the national fuel shortage). These recordings are the primary source of data for the Ground Control positions in this report. 2. 4. 1. 3 Tower Observation and Analysis of Controller Task and Non- Commu- nication Activities During several periods project analysts were stationed in the tower cab to observe and record the overall nature of operations in the cab and the spe- cific task activities of the various controller positions. General observations were made in relation to the observers' impres- sions of the working interface between control positions and the effect of the traf- fic environment and operating conditions on controller activities. During these periods a number of particularly significant events were observed and the actions taken by controllers were noted. Where the situation permitted after the events were resolved the particular problems were discussed with the controllers affected. The information gained from these general observations primarily served to sup- plement the information on controller procedures obtained through the previously discussed controller interviews. In addition, it served to supplement the detailed observations of controller non- communication activities. Several attempts were made to observe and chronologically record the activities of individual control positions in relation to all aircraft controlled over a period of one-half hour. However, these attempts were all unsuccessful for a number of reasons. Primarily, no position could be found where the observer could station himself such that he could accurately observe all activities and/or relate those activities to particular aircraft (as planned) without becoming an ob- struction to the operations of the control position he was observing or of other con- trol positions. Secondarily, the short durations of the non- communications tasks being observed did not permit the recording of all the information desired, partic- ularly the time involved, without missing or losing data for the next activity when they performed in immediate time sequence. Therefore, this approach was dropped. Instead, a two-step approach to the recording of controller activities was adopted. In the first step, the analysts concentrated on observing and record- ing the performance times for one non- communications task activity at a time. For each task activity a number of stop watch measurements of the performance times were made for three different controllers. Since ground and local control- lers were observed to be continually scanning the traffic situation visually or em- ploying the ARTS or ASDE Brite display, no attempt was made to measure this type of non-communications activity. In the second step, a number of departure and arrival flights were se- lected for a detailed Flight Trace. In performing the Flight Trace the particular flight was followed from its entry into the ASTC System to its exit from the System. For arrivals, the trace was started when the aircraft was established on the runway course and was located at approximately the 10-mile marker ring on the Local Control ARTS Brite display. The trace was completed when the aircraft docked at its gate. For departures, the trace was started in all but one case when air- craft began its pushback; in the one case, the trace was started when the flight called for its clearance. The trace was completed when the flight was handed off to Departure Control and the flight strip dropped down the Flight Strip Tubes to Departure Control. The aircraft was followed through all control positions in- volved in its passage through the system and the activities, both communications and non- communications, of each controller with respect to the flight recorded. The performance times measured for the various individual activities were utilized to derive statistical descriptions for the activities. These descrip- tions were used to compute total non- communications task activity times for each control position as a function of traffic volume. 2.4.2 Aircraft Flow Analysis The aircraft flow analysis procedure was designed to examine the movements of aircraft traffic within three major areas of the airport. These in- cluded the ramp areas and the Ground Controllers' and Local Controllers' areas of responsibility. Each aircraft moves through these areas irrespective of whether it is a departure or arrival. For the purposes of the analysis, these areas were defined as follows: 1. Ramp area - that area between the terminal concourses and inside a line defined by the outer edges of adjacent fingers. * *It was not possible to examine with any accuracy traffic flow within the cargo or hangar areas. 2. Ground Controllers' area - that area traveled by an aircraft be- tween the ramp area and end of the departure queue (waiting line) or exit from the landing runway. * 3. Local Controllers' area - the area including the departure queues and the active runways. * The variables which have been considered in the aircraft flow analysis fall into two categories, namely, independent and dependent. The dependent vari- ables which were measured include: Runway operations time Taxi service time (Nominal movement time excluding delays) Delays Safety (accident risk) The independent variables which influence the above dependent param- eters and which have been considered in this analysis include: Runway (R/W) configuration - arrivals from the east vs arrivals from the west Traffic Volume - operations /hour and other parameters to be defined later in this report Weather (visibility) conditions Gates - number, scheduling, availability Routing procedures Locations at which aircraft may be held because of the traffic flow pattern or gate unavailability for occupancy Aircraft flight phase - arrival, departure *It was recognized that these definitions may not reflect the actual division of air- craft control between these positions. However, the ASDE films which served as the major source of data for these analyses do not permit identification of the points at which actual transfer of control was accomplished in all cases. Based upon these definitions of the areas of interest, the aircraft flow analysis was effectively divided into three distinct but related areas: interviews with ATCT personnel and review of ATCT records; detailed analysis of ASDE films; and direct observation and recording of traffic movements within selected ramp areas. The independent and dependent variables considered in each of the areas are summarized in Table 2-2. Table 2-2. Examination of Aircraft Flow Variables Flow Analysis Methodology Area ATCT Interviews ASDE Film Ramp Area Aircraft Flow Variable and Records Analysis Observations INDEPENDENT Runway Configuration X X Traffic Volume X X X Weather Conditions X X Gates x , X Routing Procedures X Aircraft Hold Locations X X X Aircraft Flight Phase X X X DEPENDENT Runway Operations Time X Taxi Service Time X X Delays X X Safety (Accident Risk) X X 2. 4. 2. 1 ATCT Personnel Interviews and Records Review Extensive interviews were conducted with ATCT personnel. These interviews were conducted with members of the operations planning staff and with Watch Supervisors. The objectives of these interviews were to determine: 1. The primary runway configurations employed at O'Hare 2. The criteria used in determining the runway configurations to be employed for operations under various operating conditions 3. The operating minimums for the various runways that influence their use during lower visibility conditions 4. The aircraft taxi routing patterns employed for the various pri- mary runway configurations With seven runways oriented in several compass directions there are a large number of potential combinations that could be employed to achieve con- figurations appropriate to a wide range of operating conditions. However, many of these potential configurations are essentially variations of the primary config- urations to meet particular constraints, e. g. , runway closing for maintenance operations. Thus, the decision was made to focus on the 11 primary configurations identified by the ATCT personnel. In deriving items 1, 2 and 4 above, specially prepared illustrations of the airport surface and passenger terminal layout were used. A separate illustra- tion sheet was used for each configuration. The primary arrival and departure runways were noted as well as additional runway usage for departures and VF arrivals by general aviation and STOL commuter aircraft. Particular conditions affecting the choice of the configuration were also noted. Finally, the primary and alternate taxi routes for departure and arrival aircraft were traced on the il- lustration. The results of these interviews are provided in Section 3. Arrangements were made for a review of ATCT records to determine the degree to which various runway configurations are employed by the ATCT. It was determined that the ATCT did not compile its records in the manner desired and had not as yet compiled the runway usage data for FY1973 or calendar year 1973. Therefore, access was provided to the collection of Daily Work Summary sheets that would ordinarily be used to compile this data. Because of the volume of such data, it was determined that a sampling process would be employed. Sum- mary sheets for at least one weekday in each week within a month were selected basically at random, with the one exception that care was taken to select sheets for different days of the week within each month. The following data was extracted from the summary sheets: 1. The runway configurations employed during the normal busy hours of 7 a. m. to 11 p. m. 2. The hours within which the various configurations were employed. 3. The arrival and departure traffic volumes for each different run- way configuration period. This data was employed to compile a summary of the easterly and westerly modes of operation for the airport. 2. 4. 2. 2 ASDE Film Analysis Detailed analysis of the ASDE films provided by TSC and made during this study period served as the primary source of data for the analysis of aircraft traffic flow during the ground taxi, takeoff, and landing phases of operations. ASDE film analyses were performed in three steps with the first being a deriva- tion of overall traffic flow statistics and the last two focusing on specific aspects of the flow process; i. e. , causes and locations of aircraft holds and potentially hazardous incidents. 2. 4. 2. 2. 1 Aircraft Flow Statistics The ASDE films were made using a time-exposure control camera. A frame was taken every two seconds; one second of exposure followed by a pause of one second. A digital clock was mounted on the ASDE monitor and within the area of view. The films were then produced using a special film analysis projector providing variable speed and frame-by- frame control. The method of data extraction involved examination of the operations for one runway at a time. Each arrival aircraft was identified during its approach phase and traced in time until it reached and entered the ramp area. The ASDE films did not permit accurate examination of the aircraft movements within the ramp area. For this reason it was necessary to treat departure aircraft as "arrivals in reverse" and to trace them backward in time from takeoff to emana- tion from the ramp area. Aircraft identity and, except in some cases (e. g. , 747s), aircraft equipment type could not be determined from the film. In addition, the precision of the films did not permit separation of traffic on the inner and outer circular taxiways, except in a few cases. Table 2-3 illustrates the events for which times of occurrence were recorded for arrival and departure aircraft. It should be noted that it was not possible to obtain data on the movements of aircraft between the terminal ramp Table 2-3. Movement Events Measured for ASDE Film Analysis Arrivals Departures OL - Over Last Light TO - Turn Off Runway HI/SI; „„ . . „ H2/S2 " H°ldS HP/SP - Enter/Leave Penalty Box ER - Enter Ramp Area* LR - Leave Ramp Area HI/SI; „„ . , „ H2/S2 " H°lds EDQ/LDQ - Enter/Leave "Dept. Q" RTR - Ready to Roll STO - Start Takeoff areas and the hangar/cargo areas. * The times recorded were used to compute the taxi service time and hold delay time for each aircraft. As noted in Table 2-3 the beginning and end of each "Hold" was deter- mined for each aircraft. These "Holds" included a "Penalty Box Hold" for some arrival aircraft. This delay is attributable to gate unavailability rather than sur- face traffic congestion and a method for identification and subtraction of this type of "Hold" time from the total delay was developed. The guidelines used for iden- tification of Penalty Box Holds include location of "Hold" area associated with the following guidelines: • Aircraft stops within known areas for holding of aircraft • An arrival aircraft may occupy a holding area only once • All "Holds" whose duration was in excess of 90 seconds were assumed to be of gate nature unless the ASDE films permitted assessment of another reason for the hold. A copy of the form used for the reduction of the ASDE films is shown in Appendix B. From the times computed for each aircraft observed in an analysis period, average taxi service times and delay times were derived for the analysis period. These values were then used to compute and/or plot the average times for various traffic levels for the two different modes of operation for the airport: arrivals from the east or west. In addition, the measured data was employed to compute a value for the average number of aircraft under control in the Ground Controllers' and Local Controllers' areas using the relationship * These aircraft are handled by the Arrival Ground Controller; the level of this ground movement activity appears to be less than 10 percent of the aircraft actually measured and may be determined from the analysis of the communica- tion tape records for the above controller position. 1+ AT T. Q = Average aircraft density or number of aircraft under control N = Total number of aircraft controlled during analysis period AT = Duration of the analysis period (normally one hour) T.= Average time under control for individual aircraft 2. 4. 2. 2. 2 Ground Taxi Hold Analysis Following the derivation of the data for the aircraft flow statistics, the ASDE films were then subjected to further detailed analysis of the holds recorded (with the exception of "Penalty Box Holds"). The purpose of this analysis was to determine whether particular patterns relative to the locations at which aircraft holds are likely to occur could be discerned from the films to corroborate infor- mation developed in discussions with ATCT personnel. To accomplish this a map of the airport surface configuration was utilized. Each surface intersection was given an identification number according to an assignment scheme which distinguished between intersections on the inner/ outer circular taxiways, other taxiway/taxiway intersections, and taxiway/runway intersections. The circumstances associated with each hold (i. e. , its location and the movements of other traffic relative to the holding aircraft) were studied and the location and (judged) probable cause or reason recorded, where it could be ascertained. The reason categories used included: (1) competing traffic; (2) run- way crossing; (3) ramp congestion; (4) unknown; and (5) other. The recorded data was compiled for each analysis period, and for each mode of airport operation. The results were analyzed to determine whether a particular pattern could be observed for each of the two modes of operation and combined operations. 2. 4. 2. 3 Ramp Area Observations It was determined that the only feasible way of collecting accurate data on aircraft movements within the terminal building ramp areas was by direct ob- servation and recording of events of interest. In comparison with other data col- lection methods (e. g. , ASDE photographic recording) the manual recording of ramp area activities presents certain constraints which should be recognized. First, the observer location dictates physical limits in the size of the area which can be viewed and accurate data collected. Prior to the start of the data collection efforts, a data recording form was developed to facilitate the data collection process. A sample of this form is shown in Appendix B. The form provided for recording of the operating airline, aircraft type, gate number, the time of occurrence of various events in the move- ments of arrival and departure aircraft in the gate area (e.g. , pushback, start to taxi, begin hold) and the apparent reason for any delays. In testing the data col- lection method it became apparent that it was not practical to readily identify the time at which a jetway was removed. Consequently, this item was omitted from further consideration. The use of 35 mm camera recording techniques was also investigated. However, due to the relatively restricted viewing area of a camera (even with a wide-angle lens) from feasible observation points on the airport, it was concluded that no significant advantage would result by this means. Second, depending on the location of the observation point, the rapid identification of the specific gate at which an activity commences can at times be difficult due to obstructions (other aircraft blocking the view, for example) or due to the considerable distances and viewing angles involved. Finally, when multiple aircraft are in various stages of arrival or de- parture simultaneously, the problems associated with noting a particular event and the time of the event and immediately recording this data for the correct air- craft became rather difficult in a short period of time. The optimum method for dealing with these constraints during the ob- servation period consisted of combinations of (1) limiting the area under observa- tion, (2) proper location of the observation point, and (3) by working as a team with one observer noting the occurrence and time of an event and a second ob- server recording the data in the appropriate space on the data sheet. 2. 4. 2. 3. 1 Data Collection Observations of aircraft movements were made from three different locations which permitted coverage of the individual ramp areas. United Airlines operates a ramp tower located on top of the intersection of the E and F concourses. From this location an unobstructed view is available for the ramp areas between the D-E, E-F, and F-G concourses. The second location was at the ramp tower located on top of the intersection of the H and K concourses. This tower is oper- ated by American Airlines for control of their assigned gates. Due to the physical location of various offices within the ramp tower area (facing the H concourse), the view is restricted to the H-K and K ramp areas and the two AAL gates (H-l and H-2) located on the inner edge of the H concourse. The third location selected for observation of the G-H ramp area was located within the main terminal approx- imately midway between the G and H concourses. In the case of observations of the G-H ramp area, it was absolutely essential to use the team approach for data collection as a result of an additional factor not mentioned above. This was due to the relative illumination levels of the area under observation and within the terminal building during the early morning and early evening hours which made observations much more difficult than those from the ramp control towers. For arriving aircraft, the time of entry into the ramp area was re- corded when the aircraft physically passed the outer edge of a particular con- course. In the event of an arrival hold, the times at which the aircraft stopped taxiing and began taxiing again were recorded. The docking time was recorded as that time when the aircraft came to a halt at the gate. Aircraft type, airline, and gate number were also recorded at that time. For departing aircraft, aircraft type, airline, and gate number were recorded while the aircraft was still at the gate. Timing measurements began when the aircraft first began pushing back from the gate. Pushback was consid- ered to be complete when the tow bar was physically removed from the aircraft and the time was then recorded. The time at which the aircraft began to taxi was recorded. In the event of a departure hold at any point in movements (e. g. , dur- ing pushback or after taxi was begun) the times at which the movement stopped and was reinitiated were recorded. The time of exit from the ramp area was recorded when the aircraft physically passed the outer edge of a particular concourse. In the event of a movement hold for either arrival or departure, the apparent reason for the hold was recorded (if possible to ascertain). 2. 4. 2. 3. 2 Data Analysis For arrival aircraft two movement characteristics were computed: Ramp Service Time and Arrival Hold Duration. Ramp Service Time for "Arrivals" was defined as the duration of the time interval between time of entry and docking, including holds, if any. Arrival Hold Duration consisted of the total of all holds in the ramp area while the aircraft was entering. Ramp Service Time and Hold Duration were computed for departure aircraft as well. In addition, two other movement characteristics, Pushback Dur- ation and Engine Start Time, were computed. Pushback Duration was defined as the time difference between the start of pushback and removal of the tow bar. Engine Start Time was defined as the time interval between completion of push- back and the start of departure taxi. Departure Hold Durations included all peri- ods during which the aircraft is stopped after the initial taxi operation began. Ramp Service Time, for departures, was defined as the total time interval between the start of pushback and the time the aircraft passed the outer edge of the finger. For those aircraft which arrived and departed within the specific ob- servation period, a "Gate Occupancy Time" was derived to provide data on the length of time the aircraft physically occupied the gate. This interval was deter- mined from the time of docking to the time that pushback commenced. The resulting data was used to develop statistical distributions of these various movement characteristics. In addition, an analysis of the data was made to determine the primary causative factors for aircraft delays within the gate area. An analysis was made to determine the average ramp density (number of aircraft in the area per minute) and the short-term effect of scheduling peaks on aircraft movements in the ramp area. 2. 4. 3 Airline Operations Analysis The airline operations analysis was designed to examine those aspects of aircraft operator procedures that impact on the total operations at O'Hare and the operations of the ASTC System. The aspects of airline operations of interest include planning of aircraft schedules and gate assignment, control of gate operations, and aircraft flight crew operations. To study these aspects the air- line operations analysis was divided into two distinct but related areas: 1. Interviews with airline terminal operations management personnel and observation of operational activities 2. Interviews with pilot personnel and in-flight observation of flight crew activities 2. 4. 3. 1 Gate/Planning Control Interviews and Observations The specific objective of the interviews with airlines terminal opera- tions personnel was to obtain information related to: 1. The manner in which flight schedule and gate assignment plans are developed. 2. The criteria employed in developing the gate assignment plan and making adjustments to that plan when gate delays are experienced. 3. The procedures employed in coordinating aircraft departure from and arrival at the gates. The primary method of obtaining this information was interviews with personnel from three major airlines operating at O'Hare: American Airlines, TransWorld Airlines, and United Airlines. These airlines were selected because they were major operators at O'Hare, constituting more than 50 percent of all traffic; hence they could provide the most information on gate planning and control, they operated a variety of aircraft, and they were most subject to gate delay prob- lems. The three airlines were contacted and arrangements for the interviews made. The principals interviewed for each of the airlines were: American Airlines - Mr. Jack Woods TransWorld Airlines - Mr. Peter Constantino United Airlines - Mr. Michael Jankovich A structured questionnaire was developed for use in these interviews. It incorporated a number of questions in each of the objective areas identified above and provided for recording of the responses directly on the form. In addi- tion, the opportunity was taken to incorporate a number of questions soliciting the opinions of the interviewees on potential concepts for coordination of airline gate planning/control functions with traffic control functions in future ASTC systems. A copy of the questionnaire employed is included in Appendix C. These interviews were supplemented by observations in the airlines' planning and control facilities to gain a first-hand impression of these operations. The results of the activities were utilized to develop the functional description of the duties and responsibilities of airline personnel provided in para- graph 4. 3. 2. 4. 3. 2 Pilot Interviews and Cockpit Observations The specific objective of the interviews with pilot personnel was to ob- tain information related to: 1. The division of functional responsibilities between the members of the flight deck (cockpit) crew. 2. The procedures followed in communications with the ATCT and airlines operations. 3. The procedures followed in controlling the movements of aircraft within all phases of the flight. 4. Attitudes toward the existing ASTC System at O'Hare including both control by the ATCT and visual ground aids. Arrangements were made with American, TransWorld and United Air- lines for access to a number of pilots, including both management and line pilots. In addition, with the assistance of two of these pilots, contact was established with two general aviation pilots who agreed to provide an interview. The pilots who participated in this activity include: 1. Robert Smith, Mgmt Pilot, AAL 2. John Hub, Line Pilot, AAL 3. John Rhodes, Mgmt Pilot, TWA 4. Curtis E. Rogers, Mgmt Pilot, TWA 5. H. A. Jacobsen, Mgmt Pilot, TWA 6. Bernard Sterner, Mgmt Pilot, UAL 7. Richard Schultz, Line Pilot, UAL 8. Raoul Castro, General Aviation Pilot (Corp) 9. Robert E. Riddle, General Aviation Pilot (Corp) The structured questionnaire developed for use in these interviews was divided into two parts. The first which was completed by the pilots was a summary of his flight experience. In the second part of the interview the pilots were first asked to provide a narrative scenario of the functions performed by each flight of- ficer during departure and arrival. This was followed by detailed questions and answers covering specific aspects of interest of crew activities not previously covered by the interviewee as well as pilot attitudes toward current ASTC System operations. In addition, the opportunity was taken to incorporate a number of questions to solicit pilot opinions pertaining to potential concepts for improved visual ground guidance and transmission of clearances and control instructions to aircraft in future ASTC systems. To assist in this latter area of the interview, illustrations of potential methods of providing this information to the cockpit crew were prepared as references for the questions asked. A copy of the questionnaire employed is presented in Appendix C. These interviews were supplemented by in-cockpit observations by project staff members. Arrangements for Flight Deck Authority for two staff members were made with the assistance of United Air Lines for flights between O'Hare and Newark Airports. Depending on the availability of one or two observer seats in the cockpit for the flights flown, one or both of these staff members were in place in the cockpit to observe operations during departure and arrival phases of flight. Departure phase observations were made from the point at which the crew boarded the aircraft until the aircraft reached its enroute altitude. Arrival phase observations were made from the point at which descent was initiated until the completion of flight check procedures following the docking of the aircraft. The equipments flown during these flights included DC- 10, DC-8, and DC-8-60 series aircraft. During the flights recordings were taped of the observers' impressions of the activities of the flight crew and the situations encountered, In a few flights, detailed records were made tracing the movements of the aircraft, the activities of the crew, and communications with ATC and airline operations in time sequence. The results of the activities serve as the basis for the functional de- scriptions of flight crew responsibilities in Section 4. 3 and the flight crew work- load analysis in Section 5. 4. 2. 4. 4 Airport Management Operations Analysis The airport management operations analysis was designed to examine those aspects of the procedures followed by the O'Hare Airport management which impact on the total operations of O'Hare and the operations of the ASTC System. The aspects of airport management operations of interest included planning and coordination of airport maintenance operations, planning and coordination of snow removal operations, and coordination of emergency operations. This included coordination of these operations within the airport management organization and with the ATCT. The information in these areas was derived through interviews with airport management personnel and through review of the O'Hare Operations Man- ual and Emergency Operations Manual provided by the Assistant Airport Manager. A structured questionnaire was developed for use in the interviews. It incorporated questions covering each of the above areas of interest as well as the functional organization of the airport management. The opportunity was also taken to incorporate a number of questions to solicit the opinions of the interview- ees on potential concepts for the interface between airport management and ATCT operations in future ASTC systems. 2. 5 PROJECTION OF THE FUTURE OPERATING ENVIRONMENT AT O'HARE AIRPORT An attempt was made to obtain detailed information pertaining to pro- jections of the future operating environments of O'Hare Airport through 1985 for use in the future ASTC System effectiveness analysis. The information desired fell into the general categories of: 1. Runway construction 2. Taxiway construction 3. Terminal facilities construction 4. Traffic volumes 5. Aircraft fleet It was not possible to obtain the desired information. Therefore, it became necessary to formulate a projected environment based upon certain reason- able assumptions. Assumptions relative to future construction of runway, taxiway and terminal facilities were based upon discussions with ATCT, airline, and airport management personnel. In meetings with these personnel, various possible changes to the airport facilities which have been considered were discussed and those most probable of implementation noted. Therefore, for the purposes of the future ASTC system analysis the projected environment was assumed to include: 1. Construction of a new 9L-27R runway parallel to and north of the existing runway and use of the existing runway as a parallel taxi- way 2. Construction of a new 4L-22R runway parallel to and northwest of the existing runway and use of the existing runway as a parallel taxiway 3. Construction of a new section of taxiway connecting the 14R-32L parallel taxiway to the 4L end of the existing 4L-22R runway or future parallel taxiway 4. Construction of a new International Terminal Complex on the cur- rent site of the USAF/Air National Guard terminal facility. Another possible change in the airport facilities mentioned in discus- sions— the elimination of inner gates of the various terminal concourses and con- struction of underground facilities for passenger access to the remaining concourse areas — was rejected as being unreasonable for the foreseeable future. This is based upon the fact that gates represent revenue-producing elements for the airlines and airport and their elimination, particularly in view of revenue losses caused by the recent flight schedule cutback and increasing operating costs, would appear un- likely. In addition, prior to the cutback, operations at O'Hare were to some ex- tent gate limited, i. e. , gate delay holds were frequently encountered by arrival aircraft during heavy traffic periods. Thus, if traffic volume increases of any significance are to be considered for future O'Hare operations, reduction in the current gate capacity would be counter-productive. In fact, in 1970-71 extension of the existing concourses to provide increased gate capacity was under consider- ation by the airport management. SECTION 3 - AIRPORT CONFIGURATION DESCRIPTION 3.1 GENERAL The purpose of this section is to provide a functional description of the physical configuration of O'Hare Airport as it affects traffic operations and flow. It is also intended to serve as a background reference for the functional desciption of the ASTC System operation in Section 4. The material in this section is di- vided into descriptions of the various runway configurations and usage patterns, taxi flow patterns in relation to runway configuration in use, and the terminal facil- ities configuration. 3.2 RUNWAY CONFIGURATION DESCRIPTION 3.2.1 Runway Descriptions Figure 3-1 presents a plan view of O'Hare Airport. The north side of the field has four runway pavements; however, runway 18/36 is restricted to light aircraft departures. While the south side of the airport has the same number of major runway pavements (three) as the north side, the runway intersection ratios are appreciably different in the south than in the north. Each runway pavement, of course, can be used in two directions so that six major runways are available in each of the north and south areas. Runway identification is based upon the mag- netic heading of the runway (to the nearest 10 degrees) with suffix "L" or "R" to distinguish between the "parallels" as viewed from the aircraft. From 0800 to 2000, it is common for four primary runways to be in operation — an arrival /departure pair on the north side and one on the south side of the airport. From the layout of the runways shown in Figure 3-1, it is seen that most of the possible arrival/departure runway pairs involve intersecting run- ways. As will be shown in paragraph 5. 3. 3. 1. 3, the capacity of intersecting run- ways is determined by the ability of the controller to manage departure releases in the face of the incoming arrivals. Briefly, if the arrivals routinely cross the Figure 3-1. Current O'Hare Layout departure runway prior to turnoff, then departure releases are keyed directly to the arrivals. The difficulty of the task depends on both how quickly the arrivals cross the intersection after touchdown and how quickly the departures clear the intersection after release. The farther down the runways the intersection occurs, the greater the dispersion on roll times to the critical intersection and the lower the capacity. On the other hand, if the arrivals routinely turn off prior to crossing the departure runway, then departure releases may be handled relatively indepen- dently of the arrival traffic. This results in a sharply increased capacity over the configuration in which both arrivals and departures have long rolls to the critical intersection. Because of the importance of configuration on the operation and capacity of intersecting runways, these runway combinations have been divided into four classes for the purposes of this working paper. These classes are presented in Table 3-1. Table 3-1. Classification of Crossing Runway Configurations Crossing Run- way Configu- ration Classi- fication Arriving Aircraft Will Cross Departure Runway Departing Aircraft Will Cross Arrival Runway Examples (Arrival/De- parture Runway) Near-Near While still in air or within 2000 ft from start of touch- down zone Within 2000 ft from roll initiation • 27R/32R • 9L/4L Near-Far Same as above Roll to intersection > 2000 ft • 32L/27L Far-Far Intersection beyond 2000 ft from start of touchdown zone and arrivals routinely cross departure runway prior to turn off Same as above • 14L/4L Quasi - Independent Arrivals routinely turn off prior to intersection but a missed approach initiated just prior to touchdown may pass over the depar- ture runway Not constrained • 14R/27L • 14R/9R Landing Aids The following source data was used to identify the landing aids of O'Hare: 1. Composite Utility Drawings (Revised July 1973) 2. Pavement and Taxiway Lips (Effective Nov. 18, 1972) 3 FAA Map (No date shown) 4. FAA Airport Master Record (Date of print 5/24/73) Due to differing dates of the information sources shown, a number of possible conflicts/inconsistencies were noted and attempts made to resolve them. Although Source 3 is not dated, it does appear to be the most recent source in terms of ILS component location as well as actual runway taxiway configurations. Table 3-2 provides a summary of both electronic as well as visual landing aids deployed for the various runways. For the purpose of this table, the Cat I ILS components consist of (1) Middle Marker, (2) Glide Slope, and (3) Local- izer. The Cat II components are the same as for Cat I with the addition of an Inner Marker. Based on the above components, substantial agreement between the various sources was noted; however, the following items could not be located on Source 1, an omission considered to be due to lack of complete updating: Runway Missing ILS Component 9R Glide Slope 27L Middle Marker 14R Inner Marker 32 L Middle Marker 14L Inner Marker 32R Localizer 4L Localizer 3 > ai a, "B .5 X K X X f g g gas X x > > w &3 < > 03 < > < fa fa 03 03 \ \ 03 03 ■J J < < w fa 03 < fa fa 03 03 \ \ 03 03 < < En 03 03 fa 03 03 <3 c 1 CJ W >> 0) l"H Is O * X X X X « * .2 >> "3 % o O o * * .2 a) < o 03 0) < O 2 iH CO J g 05 5 oo 1? s o a Visual landing aids were found to be in general agreement between Sources 3 and 4 with a single exception. For runway 4L, Source 3 indicates ALS/SFL while Source 4 indicates SALSF. In addition, it has been assumed that the acronym ALS/SFL used in Source 2 is identical to ALSAF used in Source 4 and may be due to changes in the manner of usage. RVR instrumentation, as obtained from Source 3 , is available as shown in the table. The only disagreement noted from Source 4 involves a single instal- lation which serves runways 9L and 4L with an EW, 3.2.2 Runway Configuration Usage Identification of the usage patterns for the O'Hare runway configuration was based on five sources of data:* 1. Maps illustrating the primary runway usage /taxi flow configura- tions and runway operations counts for CY 1971. * 2. Discussions with O'Hare ATCT personnel. 3. Review of runway configurations observed on TSC and CSC ASDE films. 4. Review of ATCT summary Daily Work Sheet for a sample of days over a six month period, January to June 1973. 5. Chicago O'Hare Airport Air Traffic Control Tower Training Manual, Dept. of Transportation/Federal Aviation Administration, December 1973. *The maps illustrating runway configurations provided in item 2 were estimated to be at least two years old and did not include any reference to runway 4R/22L which was not completed until late in 1971. Therefore, the effort under item 2 was essentially intended to determine recent configurations data. 3.2.2.1 Runway Configurations The discussions with the ATCT resulted in the identification of eleven primary runway configurations for O'Hare operations. This does not in any way reflect all the possible configurations that could be employed where the situations dictate, e. g. , the closing of a runway requiring the use of a different configuration. Even within the eleven configurations a number of variations were identified, which basically involved the substitution of one runway for another for departures with- out changing the basic ground traffic flow pattern. The configurations identified are presented in Table 3-3. It may be noted that, for each configuration, Table 3-3 also provides a classification of the basic mode of operation for the airport, the classification of the runway opera- tions made, and the particular conditions under which this configuration may be employed. In discussing the development of the study analysis approach in Section 2 it was indicated that two modes of operation of the airport seemed apparent, i.e., Arrivals from the East and Arrivals from the West. This assumption appears to be borne out by the runway configurations shown in Table 3-3. In configurations 1 to 4 the approaches to the arrival runways indicated are essentially made from east to west, with departures also from east to west. In configurations 5 to 10 the approaches to the arrival runways (and departures) are essentially west to east. Configuration 11 has been classified as a mixed mode of airport operation since it incorporates arrivals and departures from both east to west and west to east. The significance for this configuration could not be ascertained by CSC. The decision to classify the mode of airport operations in terms of arrival direction was further borne out in discussions with ATCT personnel rel- ative to the manner in which the runway configuration to be used is chosen. 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In addition, the weather reports are posted for other tower personnel and in conjunction with changes in air- port runway configuration to prepare revised ATIS recordings. The major responsibility of the Clearance Delivery position is to de- liver the ARTCC IFR clearance to departure aircraft and to verify that the flight crew has properly received the clearance. In accomplishing this the Flight Strip Bay/ flight strips and VHF radio serve as his primary equipments. In the case of VFR departures, the duties associated with this responsibility also include ascertain- ing the desired direction and altitude of exit from the TCA and preparation of a VFR flight strip. The other responsibility of this position is to receive notifica- tion that aircraft are ready for taxi or for pushback, where the situation requires clearance to do so, and to turn these aircraft over to the appropriate ground con- trol position for these aircraft. The particular position will depend on whether or not the aircraft is a normal departure or a cargo/hangar area flight, whether or not the aircraft requires a pushback clearance, and the level of traffic at the time push- back is required. The Outbound Ground position is responsible for issuing taxi clearances to departure aircraft, including the assignment of the departure runway and route to the runway, and assuring the safe and expeditious flow of the aircraft along the assigned route. The one exception to this responsibility for departure taxi clear- ance is helicopter flights which are the responsibility of the Inbound Ground position. During both the transmission of the taxi clearances and maintenance of the traffic flow, the Outbound Ground controller is responsible for monitoring the traffic flow through visual observations or pilot position reports and to transmit the necessary control instructions or traffic advisories to resolve potential conflicts between aircraft. This position is also responsible for turning these aircraft to the Local Control position responsible for the assigned runway when the aircraft is safely established on the taxi approach to the runway. This point will vary for various runways depending on the runway configuration in use and traffic flow associated with this configuration. Under certain configurations this will require this position to assume responsibility for safely seeing aircraft across an active runway before the turnover is accomplished. Similarly, the Inbound Ground position is responsible for issuing taxi clearances to arrival aircraft, including the route to their airport destination, and assuring the safe and expeditious flow of the aircraft along the route. In discharg- ing this responsibility, this position is responsible for accommodating aircraft whose terminal gate is not available for occupancy. This requires ascertaining the availability of aircraft gates and routing affected aircraft to interim holding areas most suitable for rapid access to their gates when they become available. As noted above, this position has the responsibility for ground taxi of helicopter traffic, both departures and arrivals. In addition, the Inbound Ground position has responsibility for control of traffic between the passenger terminal and the hangar and cargo areas, in either direction. Similar to the Outbound Ground posi- tion, this position will monitor aircraft movements through visual observation or position reports to identify potential conflicts or delays in traffic flow and issue the control instructions and/or traffic advisories necessary to resolve them. However, unlike the Outbound Ground position, the Inbound Ground position has no flight strips for his traffic and has no responsibility for turning the aircraft over to another con- trol position. The major responsibility of the Local Control position is the establish- ment and maintenance of a safe and expeditious runway operations sequence. The Local Control #1 position has this responsibility for runways on the south side of the passenger terminals and the Local Control #2 position for runways on the north side of the terminals. The Local Control #2 position actually operates at the Local Control #4 work station. * In discharging this responsibility these positions are *The tower cab layout provides a number of additional work stations to allow for future expansion of the tower staff in the event that it becomes necessary. required to monitor the movements of arrival and departure aircraft visually or through position reports to determine that safe separations between arrivals and departures on the same or different runways are achieved without undue delays to these operations. This requires assuring that these operations will be completed taking the necessary control actions to maintain traffic flow when it becomes neces- sary to abort an operation. The second major responsibility of the Local Control position is to turn landed aircraft over to the Inbound Ground position for taxi to their airport destination when they are safely clear of other runway operations. In certain runway configurations this requires the Local Control position to main- tain control of aircraft and provide the necessary taxi instructions to see the air- craft across the last active runway under his responsibility. This is more fre- quently required of the Local Control #2 position. The Watch Supervisor is generally responsible for monitoring the status of surface operations and supervising the activities of the preceding control positions. Specifically, the Watch Supervisor is responsible for monitoring the local conditions affecting airport surface operations, selecting the most suitable runway configuration for use under these conditions, and coordinating this decision with the TRACON Watch Supervisor and tower cab controllers. In addition, under situations where weather or other conditions (local or external to O'Hare) result in problems of delay and surface congestion, the Watch Supervisor will determine whether departure aircraft must be held at their gates, arrivals held, or these operations carefully metered until the congestion is reduced. This decision will be coordinated with the TRACON Watch Supervisor and transmitted to tower cab personnel. 4. 2. 2. 2 Visibility Constraints of Tower Operations The operations of tower cab control positions are influenced by visi- bility conditions. The limits of visual coverage of surface operations are illus- trated in Figure 4-4 under VFR and Category I conditions. Locations at which controller visual observation of aircraft movements or position on the surface Figure 4-4. Visual Surveillance Limitations is physically blocked by airport facilities are indicated. In addition, areas in which controller visual perception of the position of aircraft is reduced because of their location relative to the tower are also indicated. The limits of visual coverage under Category II conditions are not indi- cated in this figure because of their variability. Under the best conditions when the fog is patchy, limited areas around the terminal gates may be visible. Under the worst conditions all visibility of operational areas may be lost. In addition, the visibility to flight crews of other aircraft around them may become quite limited as noted on one occasion during observations at O'Hare. The limits of radar coverage of airport traffic available to the tower control positions via ARTS Brite and ASDE Brite displays are illustrated in Figure 4-5. The limits of ARTS coverage represents the ranges at which beacon tracking is terminated by the ARTS system. With respect to the ASDE coverage , the areas in which this cover- age, has been classified as unreliable or of limited reliability are indicated. This determination was made through field tests by ATCT Operations and Airways Fa- cilities Sector personnel. In addition, the height at which ASDE coverage is lost was indicated by the Airways Facilities Sector to be 20 feet at the extreme range of the O'Hare radar. Essentially, the limits of visual coverage illustrated in Figure 4-4 have no impact on O'Hare operations. Aircraft movements within the cargo or hangar areas are not normally under control of Ground Control positions. The term normally is used because infrequently it may become necessary to move air- craft waiting for departure on 14R to another runway. Under these conditions, the aircraft may be routed through the hangar area if that is the most feasible path to the other runway, e.g. , 14L. Where the visibility of the aircraft becomes blocked on the cargo taxiway, this situation exists only momentarily. Tower controller personnel have indicated that this blockage lasts only for about two seconds. The major impact of lowered visibility conditions on the ASTC system occurs at lower end of Category I and during Category n. This impact is reflected LEGEND I 1 Unreliable ASDE Coverage ^H Limited ASDE Coverage Figure 4-5. Radar Coverage in the initiation of requests for position reports by both Ground and Local Control positions and the requirement for a transmission of runway RVR and/or rollout by Local Control. This is discussed in further detail in the following descriptions of controller procedures. 4. 2. 2. 3 Controller Operational Procedures Descriptions of the operational procedures employed by the various tower cab personnel, with the exception of the Watch Supervisor, are provided below. Flow diagrams for the major functional tasks performed by these positions are presented and serve as a reference for the discussion of the impact of weather and traffic conditions on controller operations. 4.2.2.3.1 Flight Data Figure 4-6 illustrates the flow of the two major functional tasks of the Flight Data position. The task activities shown in Figure 4-6(a) for the Posting of Flight Strips occupy the predominant part of the Flight Data position's time. Flight Strips are printed out approximately one hour before the Estimated Time of Departure (ETD) for the aircraft. Normally several flight strips are printed out at one time as well as notices for removal of strips for cancelled flights. The strips are removed from the printer and separated. Removal notices are set aside. The strips are then mounted in Flight Strip Holders so that they may be mounted in the Flight Strip Board. Before posting, the strips are marked by Flight Data. Marking nor- mally includes the following: 1. Correction of the flight level to 240, the clearance limit for O'Hare, for any flight with a ARTCC clearance above 24,000 feet. 2. Correction of the first fix to reflect the appropriate clearance limits for the ATCT. 3. Underlining the first fix to facilitate its recognition and use by the remaining controller positions. 4. Underlining or circling the aircraft type data item when the air- craft is a heavy, i.e. , takeoff weight over 300,000 lbs. This is indicated by an H in front of the equipment type (e. g. , "H/DC86/A" indicates a DC8-60 series aircraft. Aircraft considered as heavies include the B747, DC-10, L1011, DC8-60 series, and over- water versions of the B707. In the case of United Airlines aircraft additional marking is performed by Flight Data. The Clearance Delivery position is required to mark the gate number for departures on the flight strips. Because United operates a substantial number of departures from gates in both the E and F terminal courses, Flight Data marks an F in the position where the gate is recorded. If the departure is from a gate in the F concourse, then Clearance Delivery is only required to record the gate number. If the departure is from an E concourse gate, then Clearance Delivery need only add the last stroke to complete the E and record the gate number. That has the effect of minimizing the activity of the Clearance Delivery position who may have to handle calls from aircraft in close succession at the expense of the Flight Data workload. The annotated flight strips are posted in the Flight Strip Board. The strips are posted on the left side of the Board by Operator and Call Sign. For domestic passenger flights, the strips are ordered roughly alphabetically by air- line and then in numerical order by flight number. The strips for Cargo, Butler Aviation, local commuter airlines and general aviation, and International Terminal Departures are posted in separate areas reserved for these operations also by alphanumeric flight identification. When Flight Data has completed the posting of the departure flight strips, the strips for cancelled flights are removed from the Board and the Strip Holder is disposed of. Figure 4-6(b) illustrates the task sequence when Flight Data is called upon to assist Clearance Delivery in obtaining a clearance for a flight which has not been received and posted by the time the pilot calls for his clearance and in obtaining a ATCRBS code for VFR departures. With respect to obtaining a clearance, Flight Data enters the flight ID on the FDEP keyboard and requests a clearance. If a clearance for the flight is in the ARTCC computer, a strip will be printed and Flight Data will perform the strip mounting and marking as de- scribed above. When there is no clearance in the computer, Flight Data must call the ARTCC via the interphone and request a clearance. He will then manually prepare a flight strip and pass it to Clearance Delivery. If the flight has not called for taxi by the time a printed strip is received, Flight Data will process the printed strip in the normal manner and replace the written strip with it. When Flight Data is requested to obtain an ATCRBS code for a VFR departure, the code must be obtained from the ARTS computer. This requires Flight Data to walk over to the ARTS keyboard at the Local Control #1 position and enter a code request. Clearance delivery is then advised of the code for transmis- sion to the departure. To minimize the requirements for repeated transit to the ARTS keyboard and the associated delay in providing the code to the departure, it is standard procedure for Flight Data to obtain several codes (normally 10 are requested) at one time. The list of available codes is given to Clearance Delivery for his use as required. When the list nears depletion or is depleted, Flight Data obtains another. A third task of the Flight Data position not illustrated in Figure 4-6 is maintaining the currency of the ATIS. Weather reports are periodically re- ceived from the U. S. Weather Service via the Telautograph. These are normally received hourly but will be received more frequently (e.g. , every 15 minutes) under Category I and Category II conditions or when special conditions exist. Flight Data will review these reports to determine whether a new ATIS recording is required. In addition, when a decision is made to change the runway configuration, the Watch Supervisor will advise Flight Data to prepare a new ATIS. Criteria requiring the preparation of a new ATIS include: 1. Ceiling changes of 1000 feet and all changes below 6000 feet. 2. Changes in visibility below six miles. 3. Changes in approaches or arrival runways. 4. Changes in departure runways. 5. Temperature changes of three degrees or more when the temperature is above 70° F. 6. Altimeter changes of three points. Flight Data manually prepares the new ATIS and operates the ATIS console to make the new recordings. ATIS recordings are made for both de- parture and arrival operations. Among Flight Data's other duties are: 1. Posting and advising other controller positions of newly received weather reports. Telautograph received weather reports are placed on the central column of the tower cab for review by other controllers. 2. Posting and advising other controller positions NOTAMs re- ceived, including confirmation of runway /taxiway closings for snow removal or maintenance operations and removal of these restrictions. 3. Dissemination of airport operations status information to air- craft operators. When operating conditions are such that air- craft operators must be advised of decisions regarding traffic operations (e. g. , gate holds have been instituted for all departures), Flight Data will transmit the advisory via the Telautograph to similar equipments at the airlines and Butler Aviation operations desks. 4. 2. 2. 3. 2 Clearance Delivery Figure 4-7 illustrates the flow sequence for the three functional tasks of the Clearance Delivery Position. The task activities illustrated in Figure 4-7(a) for IFR Clearance De- livery occupy the predominant part of the Clearance Delivery position's time. The major portion of this time is spent in relation to air carrier passenger flight operations and is outlined in the figure in a reasonably straightforward manner. When, infrequently, no flight strip can be found for an aircraft, Clearance Delivery will advise the pilot "Standby . Your clearance is on request" and request assistance from Flight Data. Normally the pilot will advise Clearance Delivery of the terminal gate from which the flight is departing. If this information is not given it will be requested. The gate number will be recorded on the flight strip to the right of the flight call sign and aircraft type. It should be noted that the gate number is not recorded for all departures. For airlines having a limited number of gates the number is not recorded. Table 4-6 summarizes the nature of gate marking for various airlines. This gate recording activity is shown sequentially in the figure for ease of illustration, but is actually performed in parallel with the reading/pilot repeat of the clearance. The flight strip is then placed in the right hand bays of the Flight Strip Board. As in the case of the original strip posting by Flight Data, the strips are ordered alphanumerically by airline and flight number to facilitate their retrieval when the pilot calls for taxi. In the case of commuter airlines or general aviation IFR departures, Clearance Delivery will advise the pilot to "Monitor Ground Control on 121. 75 (or point 75)" and the strip placed in the left side of the Outbound Ground Flight Strip Board. f li ' — £l _ £s\ _ ^ I Pt* II? 55 to 1 l 00 1B | s 5:5 = -I" e o ^ o: co .11.81 — < Q. 4 1 4 k g •If |jl HI e - iS < 2 <5 111 i l it i L 1 j > Table 4-6. Clearance Delivery Gate Marking Airline/Operator Gate Locations Marking Format No. Concourse American 12 K Number only 2 H H and Number Air Canada 1 G None Allegheny 1 K None Braniff 2 Between C&D None Continental 2 D None Delta 8 H Number only Eastern 6 D Number only North Central 6 H Number only Northwest Orient 5 D Number only Ozark 2 F None Trans World 11 G Number only United 23 E & F E or F and Number International Carriers 13 B & C B or C and Number Commuter - Butler None The task sequence VFR Clearance Delivery is also reasonably straight- forward as illustrated in Figure 4-7 (b). For these flights Clearance Delivery must obtain the general heading and altitude at which the pilot wishes to fly out of the TCA. Normally, the departure will be cleared in accordance with the pilot's re- quest except where the altitude is below or above the VFR clearance limits for the TCA (3000 and 8000 feet respectively) or where the general direction of flight is in conflict with the current flight operations pattern. Clearance Delivery manually prepares a flight strip including the: 1. Call sign 2. Aircraft type 3. ATCRBS code assigned 4. Direction of flight 5. Letters VFR in the center of the strip. This is generally accomplished in parallel with the deli very /pilot repeat of the clearance. In the event that the ATCRBS code is not received by Clearance De- livery before the flight is turned over to Outbound Ground, he will advise Out- bound Ground of the code for transmission to the pilot. The task sequence followed for Handover to Ground Control is illus- trated in Figure 4-7(c). When departures are ready for taxi Clearance Delivery is again called. In most cases the departure does not require pushback clearance and therefore has already pushed back. Clearance Delivery simply advises the pilot to monitor the Outbound Ground frequency and places the strip in the Out- bound Ground Strip Board. In those cases where a pushback clearance is required there is some variability in the actual procedure followed by Clearance Delivery. If traffic on the inner circular is light but Outbound Ground is busy and the individual manning this Clearance Delivery position has been checked out in the Outbound Ground Position, he may issue the pushback clearance and turn the aircraft over to Out- bound Ground in the usual manner. Otherwise, with light traffic on the inner, he instructs the pilot to monitor the Outbound Ground frequency and gives the strip to Outbound Ground, advising him that the aircraft needs a pushback clearance. However, if traffic on the inner is heavy, he will instruct the pilot to monitor the Inbound Ground frequency and gives the strip to Inbound Ground, advising him that the aircraft needs a pushback clearance. This is done because traffic on the inner is likely to be primarily arrival traffic and, therefore, delays caused by the departures pushback blocking the inner will impact primarily on Inbound Ground operations. In each of the task sequences illustrated in Figure 4-7 it is shown that Clearance Delivery records the time (to the nearest minute) at which the aircraft calls for taxi. This activity is not performed for any specific traffic control function but for statistical recordkeeping purposes. The ATCT maintains records on the number of departures whose total operations time from ready-to-taxi to takeoff exceeds 30 minutes*. An infrequent diversion from the procedures described above occurs in the case of the Chicago Airways Helicopter departures from gate HI. Normally the clearance for these operations is a standing one and the aircrafts make initial contact with Inbound Ground for taxi. However, under conditions where there are delays, the normal clearance for these operations may become invalid. In this situation the procedure for a general aviation IFR aircraft departure is followed. Another infrequent diversion from normal Clearance Delivery opera- tions occurs under low visibility conditions. When calling for clearance or taxi, air carrier pilots may request information on the current general visibility and RVR/rollout levels for the runway anticipated, and the prognosis for lifting of *When the flight strip is subsequently received at a Departure Control position he will reference the recorded time to the current clock time and, allowing seven minutes for taxi (in accordance with current policy), determine whether the de- parture time exceeds the 30- minute criteria. current conditions. If Clearance Delivery is not busy, as is usual under these conditions, he will try to oblige the pilot as this information may be important in the decision to depart the gate. * In doing so Clearance Delivery must walk over to the Local Control position for that runway to determine this information from the weather instrumentation at the position. 4. 2. 2. 3. 3 Outbound Ground The flow of the major functional tasks performed by the Outbound Ground position is illustrated in Figure 4-8. Figure 4-8(a) presents sequence of activities for the task of Issuing Taxi Clearance. Upon receiving the flight strip from Clearance Delivery, the Outbound Ground position will review the strip to determine the first fix, aircraft type and departure gate as the basis for selection of the departure runway and the primary basis for the selection of the routing to that runway. Although the review of other flights and visual check of aircraft positions are illustrated in the figure as sequential activities, they are essentially accomplished in parallel with the re- view of the new strip and contribute to the runway and routing selection, respec- tively. The reason for presenting these activities as sequential is that the de- parture runway assignment is essentially automatic based on the first fix and routing to that runway is dictated by the runway configuration. As indicated earlier in Section 3. 2 aircraft departing to the north and east utilize the north- side departure runway while aircraft departing to the south, west, and southwest utilize the southside departure runway. Since each first fix is associated with a particular direction of flight, it serves as the primary basis for runway assign- ment. However, when review of the other strips (or the controllers recollection) ♦Differences in airport and airline operating minimums frequently result in de- cisions to cancel at the gate or may result in the inability of the flight to take off when it reaches the departure runway. The latter effect is discussed in para- graph 4.2.2.3.5. Ii"«l ||i|I t III! if** iilli ilil* I _ i T r ijfi 8ft i — ■! 1! III! f- .1 Is * njiil ilffi ! i 1 jfij fill % -3 LEGEND Followed Conditio Followed Conditio indicates a particular heavy level of departures to the west, westbounds with a Debuque (DBQ) first fix may be assigned to the northside departure runway. As previously discussed in Section 3. 3 routings to departure runways are basically standard for particular operating configurations. However, in cer- tain configurations potential alternate routings to the departure runways exist as described in Section 4. 3 (e. g. , to 32R counterclockwise via the outer circular and 9L-27R parallel). Where these alternatives exist and traffic is heavy via the standard route, Outbound Ground may select the alternate routing for the new de- parture. The selection of this alternative depends on the location of departure gate and type of aircraft. For the above example of 32R departures the primary routing is via the outer and bridge. However, aircraft departing from the west- side of the E concourse and the B-D concourses could be routed via the inner and 9L/27R parallel alternate with one exception. Since 747s are not permitted on the inner, such aircraft from these gates would have to be routed via the primary route. Another factor contributing to the routing selection is the existence of in-trail restrictions for departures in a particular direction. When such condi- tions exist, and the runway /taxi way usage configuration permits, Outbound Ground normally routes the affected flights to the runway via an alternate that separates them from the non-restricted departures. Using 32R departures again as an example, non-restricted departures would be sent via the primary route and restricted de- partures would be sent via the alternate. The alternative routings for the various major runway configurations have been previously described in Section 3 . 3 and will not be repeated here. The first fix also is a primary factor in the establishment of the air- craft sequence to the departure runway via the route selected. Although it is not prescribed for Outbound Ground to establish the sequence, it is normally performed as a means of assisting the Local Control positions for the departure runways. This is based on the fact that alternating departures by direction of flight after takeoff (e.g. , northbound, eastbound, northbound for the northside runways) contribute to the separation of traffic and, thereby, increase the operations rate for the departure runway. Since the first fix basically determines the direction of flight, it is utilized by Outbound Ground in sequencing or fitting the departure in- to position in the traffic flow to the aircraft. Thus, the first fixes for the aircraft already in the sequence, and their positions relative to the point at which the new departure will enter the inner/outer taxi ways after taxiing out from this gate, are referenced to determine where in the sequence the aircraft may be fitted to main- tain the alternating directions without adversely affecting the flow on the taxiway. When in-trail restrictions are in effect for particular directions of flight and where the runway /taxi way usage configuration does not easily permit the use of alternate routing for the restricted departures, Outbound Ground may attempt to sequence these aircraft in a manner that assists Local Control in achieving the restrictions (e.g. , northbound, northbound, eastbound where eastbounds are restricted). This may be particularly important, e. g. , in the case of northside departures on runway 4L where there is no runup pad in which Local Control #2 can pull off the restricted aircraft until it is appropriate to release them for takeoff. However, when traffic is heavy and Outbound Ground cannot afford the time, or when delaying the aircraft's entry into the flow will block arrival aircraft entry into the gate area from which it is departing, Outbound Ground would forego any attempt to accomplish this type of sequencing. As indicated in Figure 4-8(a), when aircraft movements cannot be visibly observed during Category II conditions, position reports may be requested from other departure aircraft on the taxiways to determine their locations as an input to the sequencing decision. When the runway, routing, and sequencing for the departing aircraft have been decided upon, Outbound Ground issues the taxi clearance for the air- craft. The clearance includes the destination runway and route, as a minimum, and then any control instructions pertinent to its entry into the taxi flow or holding at active runway crossings, where required by the operational configuration. The taxi clearance transmission may also include traffic advisories intended to facilitate the compliance with the instructions provided. The clearance is provided tersely to minimize transmission time per aircraft. A few illustrative examples of typical taxi clearances are given below: United 108 Heavy. Your runway is 32 Right via the outer and bridge. Hold short of the outer. Follow a Northwest trijet coming from your right. Eastern 411. Runway 27 Left. Left on the outer. Right turn on the North-South and East on the 27 Parallel. If you taxi now you won't be blocked by a company heavy coming from the right. Delta 112. Runway 4 Right. Via the North-South. Pass behind an Ozark DC -9 coming from your left. Hold short 9 Right. During low visibility conditions, Outbound Ground may request position reports at selected checkpoints to assist him in maintaining cognizance of the traf- fic flow. Specific checkpoints are preferential to the individual manning the position. However, interviews with a number of controller personnel indicated a significant consistency among these reporting points. The predominant re- porting points given for taxi to the various departure runways are identified in Table 4-7. The runway to which the aircraft has been assigned is recorded by Outbound Ground in the lower right hand corner of the flight strip. If the departure has been sent to the runway by an alternate route, this is also recorded on the strip for use by Outbound Ground and subsequently by Local Control for that runway. The indication of alternate routing is marked next to the runway, e. g. , for air- craft routed to 32R or 27L on parallel taxi ways the runway recording would appear as 32R 11 or 27L 11. The flight strip is positioned in the Outbound Ground Strip Board on either the left or right side of the Board: left if the departure is going to a south- side runway, right if the departure is going to a northside. The strip is positioned Table 4-7. Predominantly Preferred Checkpoints for Position Reporting During Low Visibility Conditions Destination Runway Preferred Checkpoints 4L Outer and T3 Intersection 4R Outer and Past 9R on N-S Taxi way 9L Outer and T3 9R Outer and Holding #1 on Tl at 14R/32L 14L Outer and T3 14R Outer and T3 22L Outer and On the Cargo Taxi way 22R Short of 14L/32R 27L Outer and On the Cargo Taxi way 27R Outer and At the Bridge or 9L/27R Parallel (for alternate route) 32L Outer and Holding #1 on N-S at 27L 32R Outer and At the Bridge or 9L/27R Parallel 36 9L/27R Parallel among the others on that side in accordance with its location in the sequence to the runway (with the bottom strip corresponding to the first flight in sequence. ) By ordering the strips in this manner, Outbound Ground has a rapid reference to the order of the aircraft and to their call signs when they must be subsequently contacted. The functional approach taken by Outbound Ground to the Maintenance of Safe and Expeditious Traffic Flow is illustrated in Figure 4-8 (b). Visual ob- servations of traffic movements and/or position reports received during low visibility conditions provide a basis for determination of potential conflict at an intersection or delays in the movement of his traffic (e. g. , an aircraft forced to stop momentarily behind an arrival aircraft waiting to turn off to its gate). Observation at O'Hare and review of communications recordings indicated that two distinctly different types of control approaches are employed by Outbound (as well as Inbound) Ground positions. The first may be considered to be singular control in which the controller unilaterally provides the separation or movement control required. This is accomplished by the controller issuing a "hold short" instruc- tion to which the pilots respond by stopping their aircraft at the designated inter- section. The second approach may be considered to be joint control in which both the controller and pilots share the responsibility for separation or movement control required. This is accomplished by the controller issuing a "yield type" instruc- tion to which the pilots respond by adjusting their speed of taxi rather than stopping their aircraft. These instructions normally include the type of control response desired by the controller, identification of the aircraft to which the desired maneuver is referenced, and an advisory of the direction from which the aircraft is approaching the instructed pilot. Examples of such instructions include: 1. Yield to 2. Give way to _ 3. Follow 4. Pass behind Interviews with controller personnel and review of communications recordings indicate a strong preference for the joint control approach. A major factor in the preferential use of the "yield" type instructions is that only one communication to the aircraft is required. In the case of the singular control approach the pilot must be instructed to begin taxiing again. As indicated in the figure the major criteria in the decision to issue a hold or yield type instruction is the degree of certainty with which the aircraft arrivals at the intersection involved can be ascertained. When Outbound Ground is not sure of the intersection arrival time for an aircraft he may issue a hold instruction in place of a yield instruction. This same approach is followed in the inclusion of control instructions in the taxi clearances to departures. Once the control instructions have been given or simultaneously with their transmission, the positions of the strips in the Flight Strip Board will be adjusted to reflect the new order of aircraft in the sequence to the runway. The task sequence for aircraft handover to Local Control is illustrated in Figure 4-8(c). The basic philosphy underlying the performance of this task is that the turnover is made whenever there is no longer any requirement for Out- bound Ground to work the aircraft, i. e. , it has a clear roll to the runway or end of the departure queue. Table 4-8 summarizes the specific points at which, or general areas inwhich, the aircraft are likely to achieve this status and turnover can be made for the various runways. Based upon this philosophy, the major determinants in the process are whether or not the departure must cross an active runway under the particu- lar operating configuration or whether or not there is any conflicting (or blocking) traffic in its way. When a runway crossing is required, Outbound Ground observes the operations of the Local Control responsible for that runway and determines when it is appropriate to clear the departure across the runway. The pilot is nor- mally advised to monitor Local Control frequency "when across" as part of the Table 4-8. Specific Points or General Areas at Which Turnover to Local Control May be Made by Outbound Ground Departure Runway Specific Point General Area 4L Passing T3 4R Crossing 9R 9L New Scenic/4L Intersection 9R T1/14R Intersection On 9R/27L Parallel if 14R not in use 14L Crossing 9L On 14L/32R Parallel or on New Scenic 14R Old Scenic/Bypass Intersection Bypass or 14R/32L parallel if 14R not used for arrivals 22L Outer/ Cargo Intersection On cargo 22R Across 14L National Guard Ramp or Parallel 27L Outer/Cargo Intersection On cargo 27R Bridge On 9L/27R Parallel or 32R Pads 32L Crossing 27L if departing from end of 32L Outer /Tl Intersection other- wise 32R Bridge On 9L/27R Parallel if alternate route 36 Inner/9L/27R Parallel On 9L/27R Parallel clearance transmission. Based upon the major runway configurations employed, this requirement mostly affects southside departures on runways 4R or 9R. Observations in the tower cab indicated a significant distinction in the handling of traffic departing from a location northwest of the cab (i. e. , on runways 4L, 9L, 14L/R). From his work station location Outbound Ground cannot readily observe the movements of aircraft in the area in which the Old Scenic, New Scenic, and 9L/27R parallel taxiways intersect the inner/outer taxiways. Outbound Ground was observed to pick up the flight strips for aircraft routed to these runways via the Old or New Scenic and walk over to a position in the northwest part of the cab (usually behind the Local Control #1) from which he can observe that the traffic has complied with his taxi instructions. This action becomes particularly impor- tant when operating conditions are at the lower end of Category I and when aircraft are being sent to both 9L and 14R for takeoff. In the latter, departures for both runways use the Old Scenic until those for 14R can turn left at the Bypass taxiway to taxi to the 14R/32L parallel. When Outbound Ground is assured that the traffic is free of any inter- ference (e.g. , 14R departures turned onto the Bypass), he advises the pilot to monitor the appropriate Local Control frequency. Observations in the tower cab also indicated that this assurance involves a last check of the flight strip, usually with the controller holding the strip in his hand. In passing the flight strips to the appropriate Local Control position, Outbound Ground is required to momentarily move away from his work station. He must walk over to the Local Control #1 position to place the strip in the Flight Strip Board. For the Local Control #2 position which is located diagonally across the cab from him, Outbound Ground must walk over to and place the strip on the Strip Slide behind him and to his right. In instances where he has walked over to the northwest part of the cab to observe the traffic, the strip is placed on the Flight Strip Board or Strip Slide on the way back to his position. In discharging his duties as described above, Outbound is also respon- sible for assuring the separation of his traffic from vehicular traffic traveling on or crossing the taxi ways. Since such vehicular traffic is under the control of Inbound Ground and normally yields to aircraft, Outbound Ground may issue an advisory. In addition, he must monitor the movements of his traffic to ensure that they do not enter areas closed for snow removal or maintenance operations. 4.2.2.3.4 Inbound Ground The flow of the major functional tasks performed by the Inbound Ground Position are illustrated in Figure 4-9. The sequence of activities for the task of Issuing Inbound Taxi Clear- ances is presented in Figure 4-9(a). When Inbound Ground is contacted by arrival aircraft an inbound taxi clearance is issued. Under normal circumstances this includes the route to the aircraft gate and any control or sequencing instructions that are necessary to accomplish this taxi. Although it is not specifically included in the figure, in order to simplify the illustration, the determination of the position of the aircraft and other traffic by visual observation and/or position report is an input to the routing and control/sequencing instructions given. Existing traffic conditions on the Inner/ Outer taxiways and the type of aircraft (particularly 747s and general aviation) may be factors in selecting an alternate route for the arrival, in much the same way they influenced the route selection by Outbound Ground. The routing alterna- tives for the various major runway configurations have been described in Section 3. 3 and will not be discussed further here. In addition, the relative positions and certainty of arrival at intersec- tions are considerations in the nature of the control instructions given to the arrival. As an example, for an arrival on runway 32L exiting the runway at T5 or T6, the normal routing is south on the parallel, left on T3 to the outer, andthence by the inner or outer to its gate. If Inbound Ground is not certain of the time at which the aircraft will reach the T3/Outer intersection to mix with the other traffic, he will instruct the aircraft to hold short of the Outer. Although sequencing or ordering of arrivals in the traffic flow is not a requirement for Inbound Ground, it is performed by many of the controller personnel at O'Hare. When it is feasible to accomplish this, Inbound Ground attempts to reverse the order of the arrival traffic at which the aircraft will reach the points where they would exit the Inner/Outer to their gates. The object is to allow the aircraft to peel off from the traffic as they reach their gate exits and, thus, minimize the number of aircraft that might have to stop behind an arrival if its exit from the Inner /Outer is blocked momentarily by other traffic, primarily in the ramp area in which their gate is located. Observations and data collected at O'Hare have indicated that this is not an infrequent occurrence and in one instance resulted in six aircraft being stopped on the inner taxiway. Ordinarily the Inbound Ground is provided by the arrival pilot with an indication of his location at the time initial contact is made. However, the con- troller interviews and analysis of communications revealed that such position reports must be obtained occasionally, and more often than infrequently, because they are not provided by the pilot. Under this situation the typical contact message is "O'Hare Ground. This is (aircraft call sign) with you off (runway) . " When this occurs nearly simultaneously for two aircraft from the same airline the problem is compounded. Aircraft destination gate and the availability of that gate are important factors in the taxi clearance and routing for arrivals. It is particularly important for those airlines which operate gates in more than one terminal building concourse or ramp area or which by experience are most likely to have gate unavailability problems during peak traffic periods and during or following periods of traffic delays due to poor weather/ visibility. These airlines include American, Trans World, United, Delta, North Central and internationals, with the first three frequently subject to gate delays. If the pilot directly advises Inbound Ground that his gate is unavailable, the aircraft will be routed to an appropriate holding area. If the gate given the arrival is one for the three major airlines subject to gate delays of if for other airlines there are aircraft already holding for gates, Inbound Ground normally checks to see that the gate is available. If the gate is not given, he will requestthe pilot to advise him of the gate. If the identified gate is observed to be occupied, he will ask the pilot to verify its availability and advise him. If the pilot then responds that there will be a delay the aircraft is routed to an appropriate holding area. Normally, the taxi instructions are given to start the aircraft toward its gate and the above inquiries made while he is taxiing. The basic philosophy applied in assigning aircraft to particular waiting areas is to hold the aircraft as close to their gates as possible for the conditions and operating configurations. Therefore, within the framework of this philosophy, an attempt is made to reserve the use of the T3 penalty box for use for aircraft going to the gates at United and west of the United E concourse andto use the 9R/27L parallel stub and North-South taxiways for use for aircraft going to gates east of the United terminal, primarily American and Trans World. Where the operating configuration does not permit this approach or where the pilot has advised Inbound Groundthatthe delay will be lengthy, other locations maybe used as holding areas. These areas include the run-up pads at 9L, 32R, 32L, 14R and the hangar area depending on the operating configuration. The one major rule followed in select- ing a holding area for waiting aircraft is to avoid an area from which the aircraft must cross an active runway to taxi to his gate. Because there are no flight strips for arrivals, Inbound Ground records the flight call sign and assigned gate, if pertinent, on a scratch pad. Two lists are maintained on the pad, one for arrivals from the southside runways and one for arrivals from the northside runways. In the event that it is necessary to hold an aircraft for a gate, the location at which it is holding is also recorded. For aircraft holding in the T3 penalty box, a box is simply drawn around its call sign. For aircraft waiting at other locations the specific location is recorded next to the call sign. The functional sequence followed in the task of Maintaining Safe and Expeditious Traffic Flow is presented in Figure 4-9(b). Essentially, Inbound Ground operation observes the same principles in controlling the traffic flow as discussed for Outbound Ground, including the use of hold versus yield type instruc- tions. The major difference in their performance of this task relates to the exiting of aircraft from the Inner/Outer taxiways to their gates. As noted earlier for this position, the aircraft's exit may be blocked by other aircraft, most frequently air- craft departing from gates in the same ramp area as the arrivals gate. The two factors influencing the actions taken by the Inbound Ground are the estimated time for which the blockage will exist and the amount of traffic behind the arrival. If the departure has already pushed back or is taxiing out, the delay is likely to be short and, if traffic behind the arrival is light, it may be instructed to hold or yield to the other aircraft at the exit intersection. However, if there is heavy traffic behind the arrival it may be instructed to taxi to and exit at the next inter- section, if feasible for reaching its gate. When the departure is just pushing back or there are a number of departures in the ramp area, the delay is likely to be more lengthy and Inbound Ground may provide additional taxi instructions to take the air- craft in a circular path on the Inner and Outer or to take the aircraft to an area where it can hold momentarily out of the way of other traffic (e. g. , the stub or North-South taxiways between the Outer and 9R/27L Parallel). When the arrival has cleared the Inner taxiway and entered the ramp or when under Category II conditions the pilot reports docking at the gate as re- quested, the aircraft is eliminated from the active lists on the scratch pad by In- bound Ground by striking out its call sign. There are three other functions which are performed by Inbound that are not illustrated in Figure 4-9. The first is providing control of aircraft taxiing between the terminal gates and the cargo and hangar areas in either direction. Essentially, aircraft taxiing to the terminal are treated as if they are arrivals and are provided routing and control instructions, as appropriate, to their destination gate as well as a control enroute. Aircraft taxiing from the terminal building are treated essentially as if they are departures with the exceptions that they are given clearances to the cargo or hangar area rather than a runway and fitted into the Inner /Outer traffic whenever and as soon as it is feasible to do so and controlled enroute. The second additional function is issuance of pushback clearances. As previously explained in paragraph 4. 2. 2. 3. 1 this task is performed when the traffic on the Inner, which under normal conditions is predominantly arrivals, is heavy. In accomplishing this task Inbound Ground observes the traffic movements on the Inner visually, or may obtain a position report as required under Category II condi- tions, to determine where there is a sufficient gap in the traffic to permit the push- back without significantly delaying other traffic. The clearance to push back is given and the pilot advised to monitor the Outbound Ground frequency for taxi instructions. The flight strip for the aircraft is then placed in the Outbound Ground Flight Strip Board and Outbound Ground advised that the aircraft is pushing back. The third additional function is assuring the separation of aircraft and vehicular traffic traveling on or crossing the runways. In most circumstances this will involve airport vehicles enroute or returning from snow removal or other maintenance operations on particular runways or taxiways or traveling from one work area to another. Since individual vehicles or at least the lead vehicle in an operating crew must be radio equipped, control instructions regarding these move- ments are provided via the radio channel. When the vehicles have reached or are within their work area, control is not normally exercised since the area will have previously been closed to aircraft traffic. However, Inbound Ground must monitor the movements of his traffic to ensure that they do not in error enter the closed area. 4. 2. 2. 3. 5 Local Control The performance sequence for the major functional tasks of the Local Control position is illustrated in Figure 4-10. IT ',7,r The functional sequence for the task of Clearing Arrivals for Landing is shown in Figure 4- 10 (a). The approach of arrivals is monitored on the ARTS Brite Display. De- pending on the activities of the Local Control the call sign of next arrival in the sequence may be recorded on the Arrival Log from this display prior to the pilot's contact at the outer marker or simultaneous with this contact. Where the aircraft is a "heavy" this fact is also recorded. When the approach is made under Category II conditions this fact is also recorded. This log is primarily maintained for statis- tical record-keeping purposes of the ATCT since no flights strips are available for arrivals. However, for this reason it is likely that at least the call sign and heavy indication would be recorded by Local Control to keep track of the aircraft he is working just as does the Inbound Ground position. The operations of Local Control in performing this task are reasonably straightforward under good visibility conditions as shown in the figure. At the in- bound contact the pilot is cleared to land and advised of local runway conditions such as winds (if sufficient to warrant it) and turbulence resulting from the immediately preceding landing or departure by a heavy aircraft. When the runway is wet or there is snow or ice the advisory may indicate poor braking conditions. Local Control visually monitors the landing to assure that it can be safely completed and if not to execute a missed approach. This would be required under the following conditions: 1. The preceding arrivals will not clear the runway in sufficient time. 2. The required separation between the preceding departure on the same runway or a crossing runway will not be achieved. 3. A departure on the runway was delayed because of late clearing by the preceding arrival and cannot itself clear the runway. 4. An aircraft crossing the runway will not clear in sufficient time. With the exception of a missed approach, Local Control may not have further communications with the arrival unless, and until, he makes a request of the aircraft to clear the runway at a desired exit point. This request is usually made only when the runway is being used for both arrivals and departures. In addition, this request is normally made after the aircraft has touched down. If a missed approach is given by Local Control or declared by the pilot, Local Control issues the standard heading and altitude for the maneuver and advises the pilot to contact Departure Control. A minimum flight strip must be manually prepared and dropped down the Flight Strip Tubes to Departure Control. As the visibility decreases, performance requirements for this task significantly increase. When Local Control can no longer visually observe the ap- proach to the runway from the tower cab, he will begin requesting pilots to "Report the runway lights in sight during the initial contact. " This situation may exist at low Category I as well as Category II conditions. The rationale given by controllers for this is that when the pilot can report seeing the lights he is more likely to be able to complete the landing and conversely when he cannot the potential for a missed approach increases. In addition, when the RVR decreases below 6000 feet Local Control is required to advise the pilot of the measured RVR. When visibility further decreases and the measured rollout (RVR at other end of the runway) is below 2000 feet and less than the RVR it too must be given to the pilot. These advisories are also given during the initial contact. At low Category II conditions another problem develops. Many of the airlines have established operating minimums which are below the permissible operating minimums for the aircraft. Thus, it is not unlikely for the pilot to inform Local Control that the advised minimums are belowthose of the airlines. When this occurs Local Control normally requests the pilot's intentions. If he indicates that he wants to wait for better conditions, Local Control will execute the missed approach procedure outlined above. Because the RVR and rollout can change rapidly this does not usually occur. Local Control usually, then, advises the pilot to "continue the approach and I will keep you advised". At about 1 mile from the runway, and usually before the aircraft disappears from the ARTS Brite, Local Control will advise the pilot of the current RVR and rollout at which the pilot will elect to complete or abort the landing. Under the lower visibility conditions Local Control may repeat the clearance to land when the pilot reports the lights or when the conditions have risen sufficiently to permit him to land. The task activities in the next phase of the handling of arrivals by Local Control, Handover to Inbound Ground, is shown in Figure 4- 10(b). Under normal conditions Local Control will visually observe the arrival clear the run- way. The pilot is not required to report clear, although many do. Under Category II conditions Local Control may observe the aircraft clear on the ASDE Brite. How- ever, because of the low reliability of the ASDE presentation as described in para- graph 4. 2. 2. 2, most controllers request the aircraft to report clearing. The manner in which the arrival is handled after clearing the runway differs depending on whether it must cross an active runway to taxi to the terminal gate or other destination. In those instances where there will be no runway cross- ing, Local Control, depending on the runway, may issue limited taxi instructions to the arrival to start it moving toward the terminal and avoid its blocking of that runway exit for the next arrival. At the same time the pilot is advised to contact Inbound Ground. As an example of this procedure, aircraft landing on 32L would be told "South on the parallel. Contact Ground on 121. 9" after clearing the runway. Where no limited taxi instructions are required the pilot would be advised simply to contact Ground after it has cleared. Frequently, Local Control may advise the pilot of the frequency change while the arrival is decelerating on the runway, e.g. , "(Aircraft Call Sign). Contact Ground Control on 121. 9 when clear. " Where a runway crossing is required Local Control retains the arrival until it clears the last active runway under his control. This situation most frequently is faced by the Local Control #2 position when the airport is operating in an "arrivals from the west, departures to the east" mode with 14L as the arrival runway. In this situation, the arrival is given instructions for taxi to and to hold short of the runway. In addition, Local Control normally advises the aircraft to remain on his frequency. An example of such instructions is "(aircraft call sign). Taxi south on 22 (or 18). Hold short of 9L. Stay with me. " When Local Control determines that it is safe to cross the arrival he clears it across the runway and advises the pilot to contact Inbound Ground when across. The functional sequence for Clearing Departures for Takeoff is pre- sented in Figure 4- 10(c). When flights are received from Outbound Ground, Local Con- trol will reviewthemto identify the first fix, aircrafttype, and whether the aircraft are taxiing to a runway by an alternate route. This action and visual observation of the aircraft movements serve as inputs to establishing the runway usage or takeoff sequence for the various departures. Taxi instructions are given as necessary to aircraft to establish the sequence and the flight strips are ordered in accordance with that sequence, with the order being from bottom to top in the Flight Strip Board. Under normal visibility conditions, the manner in which the departures are handled is reasonably straightforward. The most significant consideration is whether the runway is being used for arrivals. In such situations, Local Control will check the positions of the arrivals to determine whether there will be time for the takeoff before instructing the pilot to position and hold on the runway. At the time the lead aircraft is given this instruction, the second aircraft in the sequence maybe toldto followthis aircraft. A procedure followed by most of the con- trollers observed to note they have given these instructions is to make a small mark next to the runway designation on the strip or the upper right hand corner of the strip. When the pilot is instructed to position and hold he is also advised of local runway conditions as required by the situation, including turbulence from the preceding arrival on the runway or the crossing arrival runway. The positions of arrival are checked to determine when the departure can be cleared for takeoff. When the runway is being used for arrivals and de- partures, the check is made to determine that the preceding arrival is clearing the runway in sufficient time to permit the takeoff with the required separation between the departure and succeeding arrival. If this is not the case, Local Con- trol instructs the departure to taxi off the runway, if feasible, to allow the arrival to land or, if not feasible, instructs the arrival to execute a missed approach. When it is safe to do so the departure is cleared for takeoff. The issuance and recording of the departure heading are shown in Figure 4-10(c) as sequentially following the takeoff clearance for ease of illustra- tion. In actuality, the point at which this instruction is given to the departure or the heading recorded will vary with the operating situation and controller. When the departure is being used for departures only, the heading may be given to the pilot with the local conditions or as part of the takeoff clearance. The heading may be recorded on the strip (to the right of the runway notation) prior to or during its transmission. In some cases Local Control was observed recording the heading even before the departure was instructed to position and hold. However, if the run- way is being used for mixed operations, it is more likely that the heading will be issued as part of the clearance to takeoff or when the departure is in the air (if the time available for takeoff is short) and the heading recorded at that time. In the latter case, Local Control normally advises the pilot '1 will have a heading for you in the air" as part of the positioned hold/local conditions advisory communi- cation. Local Control monitors the takeoff visually to determine that it is being completed safely. In situations where the takeoff is aborted before the aircraft becomes airborne, he will determine from the pilot if an emergency exists and immediately initiate the necessary action. If there is no emergency he will instruct the pilot to taxi clear of the runway and after ascertaining the pilot's intentions either issue the necessary instruction to take the aircraft back into line for departure or start it back to the terminal. As in the task of Clearing Arrivals for Departure, the performance re- quirements for this task increase significantly as the visibility conditions decrease. The first effect noted is that, when the departure runway is being used for arrivals as well, the pilot of the lead departure aircraft may be requested to advise Local Control "when the arrival is by" in order that he can instruct the pilot to position and hold. In addition, he is likely to request the pilot to report when in position. Under lowered visibility conditions RVR and rollout must be given to the pilot as part of the local conditions advisory. For the same reason discussed with respect to arrivals, the departure pilot may not be able to take off under the existing conditions. In this case, the flight is treated similarly to an aborted takeoff as shown in Figure 4- 10(c). If the takeoff can be made, Local Control is most likely to request the pilot to report rolling, becoming airborne, and starting the turn to the departure heading as a means of monitoring the progress of the takeoff. The task sequence for the next phase in the handling of the departure, Handover to Departure Control, is presented in Figure 4- 10(d). Under normal visibility conditions, Local Control visually observes the aircraft climb out and turn maneuvers, issuing the departure heading if not given previously. Under low visibility conditions he will receive the airborne and starting turn reports from the pilot as a substitute. The latter report is most significant as it serves as cue to the issuance of the handover instructions. When the aircraft is determined to be started toward its designed de- parture heading and no further attention is required, the pilot is instructed to con- tact Departure Control and the flight strip dropped down the Flight Strip Tubes to the Departure Control position in the TRACON. Observations in the tower cab indicated that, under normal visual operations, most controllers will pick up and hold the strip for a final check when issuing the frequency change. Further attention maybe required for a departure when there maybe some possibility of safe separations between departures not being achieved. This may occur because of an unusual takeoff for the aircraft or where the departure path will take the aircraft across the path of the departure for the other Local Control positions. This latter situation may occur , for example , where a westbound departure has been routed to the northside runway for reasons discussed earlier in connection with the Out- bound Ground position. Where further attention is best provided by Departure Control, Local Control coordinates with Departure Control via the interphone when the aircraft is turned over. Otherwise, Local Control will request the necessary reports and/or issue the necessary instructions to resolve the problem and, where the situation requires, coordinate with the other Local Control position. A par- ticularly significant situation in which this additional Local Control attention is re- quired is that in which an arrival on the same runway or crossing runway must execute a missed approach and in which the heading for the standard missed approach is in roughly the same direction as the heading for the previous departure. In such situations, Local Control would be required to obtain frequent reports of the altitude status of the aircraft involved, with particular emphasis on the departure, to ensure that safe separations are maintained. Quantitative measurements of the communications and physical task activities described in the preceding paragraphs are provided in Section 5. 4. 4. 2. 3 TRACON The TRACON includes 23 operating positions. The positions are basically divided into Departure Control and Approach Control. Associated with the Approach Control position is the Parallel Approach Monitor position. Its function is to monitor aircraft making parallel approaches on Runways 14, 32, and 27 when such approaches are in effect. Figure 4-11 is an illustration of the TRACON Room layout depicting the positions of the various controller positions. Tables 4-9 through 4-11 illustrate the responsibilities and duties of arrival, departure and parallel monitor positions as they interface with O'Hare Airport operations. ] uocuo III Q 000 Id) ) p Oj CD s ^ 2 ® OB*"! '3 b fe a> cr 53 5 s < > a H CD h a o 1 CU en a 0 —i -2 ,d Cd +» o 0 ti « S O |J 1 £ 73 CD CO CD ! CO '£ I o CO ,Q o ed h to g; 73 CD < > § » 8? a 73 o y, o C +j '8 o co CO o CD O rt S-i eg cd Jd > «n o < 1 £ § 2 s § £# +> cd £ — Sh "3 cd u ■a 2 h _ O «j cd £ 5h o ^ 73 >> m g "3 ® u Pi en rt CO CD CD b a SIS o pj 03 & CD o £ CU sj Cd £ 1 o O CO CD f-i CD ^ 'I K "8 5 o o TJ CD co >> p ed s '3 & 02 ffi *» < > £ w g CO 1 "3 O ej h 1 o s u £ u ed CD ed PI o u 0 o u 0) CD Ctf CO CD 3 a 0 1 3 O CD CD "3 CD o CD td a o & T3 C- 3 xs o > a o § ft 0 ed "3 "ed o o T3 CD I a a o ^ -2 '3 o CD «S to o u g | CD o CO < h « ed h ps 2 CO PI o '% 3 co | CD co CO '55 O S-i o o CD CO CO 2 a o CD o ed o >> *H o 'ed c e| "ed « o 'ed > CD o CD >> a. P ja © 1 "ft O Q« 1*1 a '3 b fc o cr pj n o W < > e 73 CD 1 "3 _■ ro i « s Rj X ft g S S S cd o SU Sh 1 s ^ g 3 O 73 S-i a CD fl CD Q 73 s § CD a 03 o o >> O § 3 CD cd M « o CD CD O CO a ?H 3 o o S 2 C8 3 .2 o u co 43 "S a a o CO CD o c < CQ % s 5 u o ft 73 3 o O "c3 JO O CD a co Bj o o c o o CD 3 CO CD CD DO CO < O u •s O 73 CD .' .s 'Go '3 ' § B < CO CD .2 1 £ S o 1 JEj 'co o a, +j as "3 d a h ^3 CD a! ,„ tf 3 a .5 § 31 3 2 TJ 0) to 3 a« ^ en s I SI 4. 3 AIRLINE FUNCTIONS 4.3.1 General Responsibilities The airlines are the major source of aircraft traffic at O'Hare. The manner in which they discharge their responsibilities can significantly impact the operations of the overall ASTC System, and the performance requirements placed on control positions in the ATCT. This is particularly true in the case of the major airlines that contribute more than 50 percent of the traffic (i.e. , United, Trans World, and American) and those other airlines that operate a significant number of flights (i. e. , Delta, Eastern, North Central, Northwest Orient, and Ozark) from the passenger terminal. As an example, the impact of airline opera- tions on the ASTC System is most felt when disruptions of flight schedules are experienced or delays in the scheduled departure of flights result in the unavail- ability of gates for arrival aircraft. The effect of gate unavailability on inbound ground operations was discussed in the previous section. Therefore, the following discussion is addressed primarily to these major organizations, with exceptions noted. The responsibilities of the airlines include: 1. Establishment of a plan and schedule for the allocation of passen- ger terminal gates for departure and arrival operations (with the exception of Ozark which does not use nose-in parking at their two gates). 2. Monitoring adherence to this plan with respect to the basic flight operations schedule and the existing conditions and adaptation of the gate assignment plan as required. 3. Advising pilots on arriving flights of their assigned gates and occupancy availability. 4. Controlling the pushback and start-up departures and the move- ments of departure and arrival aircraft within the ramp areas. * *This applies to all airlines. 5. Establishing contact with the ATCT for entry into and passage through the system. * 6. Advising the ATCT of the status of aircraft equipment and airline facilities that impact on the requirements for control of the air- craft. * 7. Adherence to control instructions provided by the ATCT. * 8. Adherence to rules governing the movements of service vehicles on the airport surface. * Responsibilities 1 to 4 are discharged by operations personnel located within the terminal facility or at the gates. Responsibilities 5 to 7 are discharged by aircraft flight deck (cockpit) personnel. Responsibility 8 is discharged by the operators of service vehicles. The remainder of this discussion of airline functions is related to terminal operations and flight deck personnel. The information related to terminal operations planning and control was obtained through interviews with the major carriers and observations of their facilities. Therefore, it may not reflect in all details the operations of other carriers. The information related to flight deck functions was also obtained through interviews with pilots for the major carriers. However, it is believed that the description of these functional operations reason- ably reflects the operations of flight deck personnel in most respects. 4.3.2 Airline Terminal Operations The airline terminal operations functions which are directly related to the planning and control of aircraft operations are gate scheduling and control and gate operations. These functions are normally performed by separate operating organizations whose activities are coordinated with one another by procedural methods. The performance of these functions by the various personnel involved is described below. *This applies to all airlines. 4.3.2.1 Gate Scheduling and Control Flight scheduling is essentially accomplished by schedule analysts working with information provided by the Marketing Department and with specific facilities criteria provided by the individual stations served by the carrier. The information thus developed provides the necessary input to determine the type of aircraft to be utilized and the specific schedules to be implemented for the various routes. The operating units responsible for gate assignment at O'Hare are the Ramp Service Departments. These units are essentially responsible for planning and day-to-day management for the activities related to the various gate areas. Typical of these activities are passenger and cargo planning, gate/flight planning, load planning (weight and balance), passenger flight processing (including updating of the flight information displays within the terminals), advanced departure proc- essing (including updating of the flight information displays within the terminals), advanced departure processing, maintaining and updating a gate assignment board, inbound flight monitoring, and ramp control operations. Gate assignment /schedule planning is accomplished by manual means and, except for minor differences in requirements due to holidays, weekends, etc. , these schedules remain essentially constant for extended periods of time. Major revisions have, in the past, been effected in the spring and fall when day- light saving time changes are instituted. Figure 4-12 illustrates a typical gate assignment plan for the hours 1400 to 2400 provided by United Airlines for the period beginning January 3, 1974. * The plan indicates the flight number, type of equipment (by the letters following the flight number), and whether the flight is an originating, terminating, or through flight. Originating flights are shown with no closing bracket on the right, terminating flights with no closing bracket on the left, and through flights with closing brackets on both ends. 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